Is there any USB Network Adapter available for Mac that works with Big Sur?
TPLink has many to choose from, eg.

Archer T3U Plus

The downside, is they don’t even sign their drivers or installer and force you to relax security on Catalina, but they seem to have the newest drivers even though they haven’t said explicitly they support Big Sur. Be sure you can return them until they support Big Sur officially if you are on a tight budget or can’t pre-test them.