Ok, I can now answer my own question as I tried it out with the TrustKey T110 Security Key:
YES! USB security keys do work with Avast Secure Browser in Normal-, as well as in Bank Mode.
However you need either Google Chrome, Microsoft Edge, Mozilla Firefox or Apple Safari to set it up with the website you want to use the key with, because it looks like certain programming procedures have to be performed that are blocked in Bank Mode. (Note: I did not try to set it up with the Avast secure Browser in Normal Mode. I used Chrome).
But once it's set-up, the USB Security Key works with Avast Secure Browser and in Bank Mode as well. At least for me with Windows 11.
