Unable to open SDLXLIFF files in Studio 2021 after uninstalling Studio 2017 and 2019

After uninstalling Studio 2017 and 2019, no default program was assigned to the file type SDLXLIFF (under Windows 7). I selected Studio 2021 as the default program but I cannot open SDLXLIFF files; another instance of the program starts but no files open in Studio.

Repair installation didn't help. I uninstalled and re-installed Studio 2021 but it didn't help either.

(I reinstalled Studio 2019, and it opens SDLXLIFF files.)

Urgent help is needed.

Sandor