diff --git a/.github/workflows/release-windows.yml b/.github/workflows/release-windows.yml
index efc8ee2807d..e20149a7eec 100644
--- a/.github/workflows/release-windows.yml
+++ b/.github/workflows/release-windows.yml
@@ -27,7 +27,7 @@ jobs:
     env:
       # see https://www.pcre.org/original/changelog.txt
       PCRE_VERSION: 8.45
-      QT_VERSION: 5.15.2
+      QT_VERSION: 6.8.0
 
     steps:
       - uses: actions/checkout@v4
@@ -69,11 +69,12 @@ jobs:
           tools: 'tools_opensslv3_x64'
           cache: true
 
+      # TODO: build with multiple threads
       - name: Build x64 release GUI
         run: |
           :: TODO: enable rules?
           :: specify Release build so matchcompiler is used
-          cmake -S . -B build -DCMAKE_BUILD_TYPE=Release -DBUILD_GUI=On -DWITH_QCHART=On -DBUILD_ONLINE_HELP=On || exit /b !errorlevel!
+          cmake -S . -B build -DCMAKE_BUILD_TYPE=Release -DBUILD_GUI=On -DUSE_QT6=On -DWITH_QCHART=On -DBUILD_ONLINE_HELP=On || exit /b !errorlevel!
           cmake --build build --target cppcheck-gui --config Release || exit /b !errorlevel!
 
       - name: Deploy app
@@ -82,13 +83,24 @@ jobs:
           del build\bin\Release\cppcheck-gui.ilk || exit /b !errorlevel!
           del build\bin\Release\cppcheck-gui.pdb || exit /b !errorlevel!
 
+      - uses: actions/upload-artifact@v4
+        with:
+          name: deploy
+          path: build\bin\Release
+
       - name: Matchcompiler
         run: python tools\matchcompiler.py --write-dir lib || exit /b !errorlevel!
 
+      # TODO: build with multiple threads
       # TODO: build with boost enabled
       - name: Build CLI x64 release configuration using MSBuild
         run: msbuild -m cppcheck.sln -t:cli -p:Configuration=Release-PCRE -p:Platform=x64 || exit /b !errorlevel!
 
+      - uses: actions/upload-artifact@v4
+        with:
+          name: bin
+          path: bin
+
       - name: Compile misra.py executable
         run: |
           pip install -U pyinstaller || exit /b !errorlevel!
@@ -103,13 +115,18 @@ jobs:
           copy addons\dist\misra\*.* win_installer\files\addons || exit /b !errorlevel!
           copy bin\cppcheck.exe win_installer\files || exit /b !errorlevel!
           copy bin\cppcheck-core.dll win_installer\files || exit /b !errorlevel!
-          mkdir win_installer\files\help || exit /b !errorlevel!
+          :: mkdir win_installer\files\help || exit /b !errorlevel!
           xcopy /s gui\help win_installer\files\help || exit /b !errorlevel!
           del win_installer\files\translations\*.qm || exit /b !errorlevel!
           move build\gui\*.qm win_installer\files\translations || exit /b !errorlevel!
           :: copy libcrypto-3-x64.dll and libssl-3-x64.dll
           copy %RUNNER_WORKSPACE%\Qt\Tools\OpenSSLv3\Win_x64\bin\lib*.dll win_installer\files || exit /b !errorlevel!
 
+      - uses: actions/upload-artifact@v4
+        with:
+          name: collect
+          path: win_installer\files
+
       - name: Build Installer
         run: |
           cd win_installer || exit /b !errorlevel!
@@ -125,28 +142,26 @@ jobs:
           name: installer
           path: win_installer/Build/
 
-      - uses: actions/upload-artifact@v4
-        with:
-          name: deploy
-          path: win_installer\files
-
       - name: Clean up deploy
         run: |
-          del win_installer\files\addons\*.dll || exit /b !errorlevel!
-          del win_installer\files\addons\*.pyd || exit /b !errorlevel!
-          del win_installer\files\addons\base_library.zip || exit /b !errorlevel!
-          rmdir /s /q win_installer\files\bearer || exit /b !errorlevel!
+          @echo on
+          :: del win_installer\files\addons\*.dll || exit /b !errorlevel!
+          :: del win_installer\files\addons\*.pyd || exit /b !errorlevel!
+          :: del win_installer\files\addons\base_library.zip || exit /b !errorlevel!
+          :: rmdir /s /q win_installer\files\bearer || exit /b !errorlevel!
           rmdir /s /q win_installer\files\help || exit /b !errorlevel!
           rmdir /s /q win_installer\files\iconengines || exit /b !errorlevel!
           rmdir /s /q win_installer\files\imageformats || exit /b !errorlevel!
-          rmdir /s /q win_installer\files\printsupport || exit /b !errorlevel!
+          :: rmdir /s /q win_installer\files\printsupport || exit /b !errorlevel!
           rmdir /s /q win_installer\files\sqldrivers || exit /b !errorlevel!      
           ren win_installer\files\translations lang || exit /b !errorlevel!
           del win_installer\files\d3dcompiler_47.dll || exit /b !errorlevel!
-          del win_installer\files\libEGL.dll || exit /b !errorlevel!
-          del win_installer\files\libGLESv2.dll || exit /b !errorlevel!
+          del win_installer\files\dmake.exe || exit /b !errorlevel!
+          del win_installer\files\dmake.pdb || exit /b !errorlevel!
+          :: del win_installer\files\libEGL.dll || exit /b !errorlevel!
+          :: del win_installer\files\libGLESv2.dll || exit /b !errorlevel!
           del win_installer\files\opengl32sw.dll || exit /b !errorlevel!
-          del win_installer\files\Qt5Svg.dll || exit /b !errorlevel!
+          del win_installer\files\Qt6Svg.dll || exit /b !errorlevel!
           del win_installer\files\vc_redist.x64.exe || exit /b !errorlevel!
 
       - uses: actions/upload-artifact@v4
diff --git a/win_installer/config.wxi b/win_installer/config.wxi
index 6a6883bea18..7bc613d1669 100644
--- a/win_installer/config.wxi
+++ b/win_installer/config.wxi
@@ -9,11 +9,6 @@
   <?define AddonsDir = "files\addons" ?>
   <?define QtDllDir = "files" ?>
 
-  <?if $(var.Platform) = x64 ?>
-    <?define CrtMergeModule = "$(env.VCINSTALLDIR)Redist\MSVC\v143\MergeModules\Microsoft_VC143_CRT_x64.msm" ?>
-    <?define PlatformProgramFilesFolder = "ProgramFiles64Folder" ?>
-  <?else?>
-    <?define CrtMergeModule = "$(env.VCINSTALLDIR)Redist\MSVC\v143\MergeModules\Microsoft_VC143_CRT_x86.msm" ?>
-    <?define PlatformProgramFilesFolder = "ProgramFilesFolder" ?>
-  <?endif?>
+  <?define CrtMergeModule = "$(env.VCINSTALLDIR)Redist\MSVC\v143\MergeModules\Microsoft_VC143_CRT_x64.msm" ?>
+  <?define PlatformProgramFilesFolder = "ProgramFiles64Folder" ?>
 </Include>
diff --git a/win_installer/cppcheck.wxs b/win_installer/cppcheck.wxs
index 731105411fa..984003eb6e8 100644
--- a/win_installer/cppcheck.wxs
+++ b/win_installer/cppcheck.wxs
@@ -13,6 +13,7 @@
     <Media Id='1' Cabinet='Cppcheck.cab' EmbedCab='yes' CompressionLevel='high' DiskPrompt='CD-ROM 1' />
     <Property Id='DiskPrompt' Value='Cppcheck installation [1]' />
 
+    <!-- TODO: what is DiskId for? It is used inconsistently -->
     <Directory Id='TARGETDIR' Name='SourceDir'>
       <Directory Id='System32' FileSource='SystemFolder' />
       <Directory Id='$(var.PlatformProgramFilesFolder)' Name='PFiles'>
@@ -36,16 +37,16 @@
             </File>
             <File Id='onlinehelpqhc' Name='online-help.qhc' Source='$(var.GuiHelpDir)\online-help.qhc' />
             <File Id='onlinehelpqch' Name='online-help.qch' Source='$(var.GuiHelpDir)\online-help.qch' />
-            <File Id='Qt5Coredll' Name='Qt5Core.dll' Source='$(var.QtDllDir)\Qt5Core.dll' />
-            <File Id='Qt5Guidll' Name='Qt5Gui.dll' Source='$(var.QtDllDir)\Qt5Gui.dll' />
-            <File Id='Qt5Helpdll' Name='Qt5Help.dll' Source='$(var.QtDllDir)\Qt5Help.dll' />
-            <File Id='Qt5Sqldll' Name='Qt5Sql.dll' Source='$(var.QtDllDir)\Qt5Sql.dll' />
-            <File Id='Qt5Widgetsdll' Name='Qt5Widgets.dll' Source='$(var.QtDllDir)\Qt5Widgets.dll' />
-            <File Id='Qt5PrintSupportdll' Name='Qt5PrintSupport.dll' Source='$(var.QtDllDir)\Qt5PrintSupport.dll' />
-            <?if $(var.Platform) = x64 ?>
-              <File Id='Qt5Chartsdll' Name='Qt5Charts.dll' Source='$(var.QtDllDir)\Qt5Charts.dll' />
-            <?endif?>
-            <File Id='Qt5Network.dll' Name='Qt5Network.dll' DiskId='1' Source='$(var.QtDllDir)\Qt5Network.dll' />
+            <File Id='Qt6Coredll' Name='Qt6Core.dll' Source='$(var.QtDllDir)\Qt6Core.dll' />
+            <File Id='Qt6Guidll' Name='Qt6Gui.dll' Source='$(var.QtDllDir)\Qt6Gui.dll' />
+            <File Id='Qt6Helpdll' Name='Qt6Help.dll' Source='$(var.QtDllDir)\Qt6Help.dll' />
+            <File Id='Qt6Sqldll' Name='Qt6Sql.dll' Source='$(var.QtDllDir)\Qt6Sql.dll' />
+            <File Id='Qt6Widgetsdll' Name='Qt6Widgets.dll' Source='$(var.QtDllDir)\Qt6Widgets.dll' />
+            <File Id='Qt6PrintSupportdll' Name='Qt6PrintSupport.dll' Source='$(var.QtDllDir)\Qt6PrintSupport.dll' />
+            <File Id='Qt6Chartsdll' Name='Qt6Charts.dll' Source='$(var.QtDllDir)\Qt6Charts.dll' />
+            <File Id='Qt6Network.dll' Name='Qt6Network.dll' DiskId='1' Source='$(var.QtDllDir)\Qt6Network.dll' />
+            <File Id='Qt6OpenGL.dll' Name='Qt6OpenGL.dll' DiskId='1' Source='$(var.QtDllDir)\Qt6OpenGL.dll' />
+            <File Id='Qt6OpenGLWidgets.dll' Name='Qt6OpenGLWidgets.dll' DiskId='1' Source='$(var.QtDllDir)\Qt6OpenGLWidgets.dll' />
             <File Id='libcrypto.dll' Name='libcrypto-3-x64.dll' DiskId='1' Source='$(var.QtDllDir)\libcrypto-3-x64.dll' />
             <File Id='libssl.dll' Name='libssl-3-x64.dll' DiskId='1' Source='$(var.QtDllDir)\libssl-3-x64.dll' />
           </Component>
@@ -56,7 +57,7 @@
           </Directory>
           <Directory Id='QtStylesFolder' Name='styles'>
             <Component Id='QtStyles' DiskId='1' Guid='$(var.qtstylesGUID)'>
-              <File Id='qwindowsvistastyledll' Name='qwindowsvistastyle.dll' Source='$(var.QtDllDir)\styles\qwindowsvistastyle.dll' />
+              <File Id='qmodernwindowsstyledll' Name='qmodernwindowsstyle.dll' Source='$(var.QtDllDir)\styles\qmodernwindowsstyle.dll' />
             </Component>
           </Directory>
           <Directory Id='TranslationsFolder' Name='lang'>
@@ -229,6 +230,7 @@
     </Feature>
 
     <MajorUpgrade DowngradeErrorMessage='Downgrade is not allowed'/>
+    <!-- TODO: remove old workarounds -->
     <!--Remove some pre 1.57 versions which can't be upgraded with MajorUpgrade-->
     <InstallExecuteSequence>
       <Custom Action='UninstallOld152' After='InstallFinalize'>NOT Installed</Custom>