Visual Studio 2022 Version 17.11.5 + latest VS Tools 3.3.1.1. Steps to reproduce:
1. Create a default widget application from template
2. Double click .ui file and confirm that it is by default opened by designer
3. Modify the .ui file, e.g. add some controls, and then save it and close designer tab (or window if you detached it)
4. Build and the run the application and confirm it runs perfectly
5. Kill the application and try to double click .ui file again, it is opened as XML file.
6. Right click .ui file and explicitly choose to open it with designer, the following error pops up:

The problem now is that you cannot further design .ui file anymore.