Environment is VS 2022 Version 17.11.5 + the latest VS Tools 3.3.1.1. The steps to reproduce are:
1. Create a default widget application from template.
2. Double click the automatically generated .ui file - it appears in designer correct in the first place. You can put something arbitrary there.
3. Save the change, close the designer tab and then build and run the app.
4. Kill the app and try to double click the .ui file again - it is then opened as a XML file by default. When you right click the .ui file and try to explicitly open it with Qt Widget Designer, such error pops up: