Not fixed yet, and no ETA. Here is the primary thread for this in the Community forum: https://support.box.com/hc/en-us/community/posts/360051323454-Box-Drive-s-system-extension-failed-to-load?page...
I have MacbookPro with M1 chip and Big Sur. Reading the above, expecting Beta fix in early 2021 - any updates from the development team? I would like to volunteer to beta test.