MS Office LTSC Pro Plus 2021: Not running, not repairing, not uninstalling

Hi guys,

since Monday none of my MS Office programs is working anymore. I'm unsure what caused the issue, but here is what I tried and found out so far:

• If I try to run Word or Outlook or whatever, I get Error 0x426-0x0
• The root cause appears to be that the "Microsoft Office Click-to-Run Service" no longer works. If I try to start it manually, I get Error 1067.
• When I try to run the online repair I get Error 30068-44 (1715)
• If I try to uninstall Office for reinstallation I get the same Error 30068-44 (1715)

Any ideas on what I should do? I can't reinstall the entire operating system just to get Office back.

Thanks a lot in advance!