I used a prepaid card from the same carrier i usually have. i did not fully deactivate the second e-SIM but switched the reception of it off.
Never change a running system. I have no idea if the phone falls back into a malfunction if i would fully remove the prepaid e-SIM which is now in my phone. Does that answer you question?
A side effect of this operation is, that the 5G and 4G reception is not only more stable it's remarkably stronger than ever before, even stronger than in my iPhone 13 Pro MAX.
By the way: I was again in the apple store today , and they confirmed that they made a bug-report to the software development. It may be that they fix the problem with one of the next IoS releases.