I am much with GraniteStateColin... I have updated to 21H1 (via the Insider route), and it has unfortunately made no difference to the Brio Hello problem on my desktop, which had been working before 20H2. I too think it is probably Logitech's responsibility now.
At some point, I'll upgrade my desktop with a new motherboard and system, maybe AMD Ryzen instead of Intel next time. Anyway, I'm optimistic that the BRIO will start working again for Hello facial recognition following a full, clean install. In the meantime, I still use the BRIO for video calling and use a fingerprint scanner for Hello login.
Did you try IMRJS's December 28 suggestion? It worked like a charm for me. I tried all the other solutions and none worked. I wasn't willing to do a clean install on my Surface pro 7+ (because I just got the dang thing).