SUMMARY
In Dolphin, when you right-click, Open With, select an app and "Remember application association", it's not always working as expected. For certain file types, this setting gets ignored. I was having success setting app for certain file types like video files, whereas for other types, like .sln files, it has never worked for a long time (not in Plasma 5, not in Plasma 6, not on a brand new system install).


STEPS TO REPRODUCE
1. Create file "test.sln"
2. Click on it, Kate opens.
2. Open With, select an app such as Rider, click "Remember application association". Rider opens.
3. Close it. Click the file again, Kate opens instead of Rider!
Going a step further
4. Open Default Applications
5. Create a new mime type: application/Rider, with file *.sln
6. Try again, same result.


OBSERVED RESULT
The selected application is ignored.

EXPECTED RESULT
The selected application should open.

SOFTWARE/OS VERSIONS
Linux: Garuda Linux
KDE Plasma Version: 6.0.5
KDE Frameworks Version: 6.0.5
Qt Version: 6.7.1

ADDITIONAL INFORMATION

~/.config/mimeapps.list contains the new custom mime type at the beginning of the list. If I manually move it to the end of the list, then it works. It kind of looks like the file has multiple mime types at the same time that override each other? If I search ".sln" in Default Applications, only my new Rider profile shows up. It's a fresh new system setup.