I tried using a SanDisk USB Flash ("thumb") drive as an alternative Time Machine backup device on my daughter's 2020 Intel MacBook Air (Catalina) and my 2020 Apple Silicon MacBook Air (Big Sur). It worked when directly connected to a 2011 MacBook Air (High Sierra), but when connected to an Anker USB-C hub it kept disconnecting:
Saturday, January 23, 2021
Don't blame your hub when your USB Flash (thumb) drive disconnects from your Mac
I was pretty annoyed with the Anker hub and decided to return it, but then I tried it on my 2016 MacBook Air (Mojave) with a rock solid old Elgato Thunderbolt 2 Hub. The same thing happened there!
So I can't blame the Anker hub too much. I canceled my Amazon return. The bug is probably some mixture of faults in macOS, the processor in Flash drives, and some global Hub/USB flaw.
It would be interesting to test Apple's hub-equivalent dongle -- the USB-C Digital AV multiport adapter.