Just filed FB7835962.
Thank you, Systems Engineer , for your comment posted 1 day ago:
"The screen capture service is a system-wide service (not a per-user service) and system-wide services should only be modifiable by an administrator. Starting with macOS Big Sur, granting access to screen recording will require admin authentication. We do understand how important this control is, and we expect to have an alternate solution for many organizational use cases in a later seed. "