Videos von Fuji-Kamera in Lightroom Classic

My LR 11.4.1 / Mac OS 12.4 / Macbook Pro (15" 2019) and my LR 11.4.1 / Windows 10 imports and plays that sample video without problem, which indicates its a problem more specific to your configuration (not a general problem with the video itself or LR's ability to handle its subformat).

Suggested next steps:

1. In Preferences > Performance, click the button Video Cache Settings > Purge Cache.

2. Reboot the computer.  Can you import a new video and play it in LR?

3. In LR, do the menu command Help > System Info (Hilfe > Systeminformationen) and copy/paste the first ten lines here.

4. If you have another disk, e.g. an external USB drive, try putting a copy of the video there and importing it with the Add option (i.e. keeping the imported video on that disk).  This will rule out the possibility of problems with the current disk (it doesn't sound likely, but we should rule it out).