Thanks ZeXx86 for the offer to upgrade my Wifi-module.

1) Yes, I would definitely prefer to leave that job for you experts.
Guess this is the place to send it: https://www.spirit-system.com/contact.php#

2) Alternatively I may buy a new Wifi-link module from your e-shop if you can confirm that the Wifi-link modules sold now are compatible with the Spirit2 units?

3) I may also be able to do the upgrade myself (prefer not to) but in case: what are the specs?

End of the BigSur-story for me:

- Reinstalled BigSur on my MacBook Pro 2015, same issue on the fresh BigSur- innstall.
- Rolled back OS to Catalina, everything worked normally…

Conclusion:
Unfortunately couldn’t make the USB-programming cable work on my mac with BigSur, and never figured out why.

Thanks a lot to all of you who tried to help!