Hello,
I've been able to replicate this bug multiple times, and it is guaranteed to happen every time. Here's the sequence of events that produces it:
1) Import transcript file (.srt)
2) When prompted to import the related video file, yes is chosen.
3) Finder pops up to select the associated media file, and it is selected.
4) MAXQDA prepares and imports the file.
5) The multimedia window shows up with the imported media file.
6) When the multimedia window is closed, MAXQDA freezes (spinning beachball/pinwheel cursor).
7) Force quit MAXQDA, reopen. All files have been successfully imported and MAXQDA is usable again.
Version: MAXQDA 2020
System: Mac OS X 11.0 (Big Sur)