Thanks for your reply!
I just had a call with the support. They could not reactivate my licence. The problem is, like you mentioned, that I have a Win7 licence and after the "hardware change" (which wasn't even a hardware change, just a BIOS update...) I can not "upgrade" to a Win11 licence.
Actually I am really frustrated now, how can this be?
I upgraded my Win7 licence quiet some time ago and I didn't even change my hardware and now my licence is gone.
The only option the support told me is to buy a new license...
BIOS is firmware, which means it is extremely low-level software which provides the I/O interface between the lowest level (direct to hardware) and the mid-level Operating System. So yes, updating your BIOS is equivalent to changing out your motherboard. It is absolutely no different from changing out your whole motherboard. Whoever told you to update your BIOS regularly, without absolutely needing the BIOS update to fix system crashes, hangs, or to support a new CPU/APU or GPU, should be shot in both knees because that's what they did to you by giving you witlessly bad advice.
Niklas B1 already pointed out that Microsoft no longer offers free upgrades from Windows 7 licenses to Windows 10 or Windows 11 licenses. I'm not sure why Niklas uses the phrase "closed the loophole" as if this was a hack or exploit, when it was literally an aggressive and intrusive marketing ploy which Microsoft nagged the actual Hell out of every Win7 user to commit to accepting, but it's not at all surprising that they took the "incentive" away this long after discontinuing support (and hamstringing with deliberately sabotaged updates) for Win7.
In case you have a separate HDD you can test out, you can try re-installing Win7 with that license and then I suspect you will have to use the telephone activation option. Once the new Win7 installation is activated, you can try re-installing Win10 and see if it will activate on the "Upgrade Path." If Niklas B1 is right, though, this won't work.