Fresh Install s2Member Pro = Critical Error

Cannot install s2Member Pro (version 210526). After installing the latest Framework (version 210526) first, then Pro version, site crashes and gives this error “There has been a critical error on this website.”

Even tried changing permissions to s2Member Pro to 777 - no luck.

Installations = (same error whether installing via WordPress and FTP)
WordPress version 5.7.2 (latest as of July 11, 2021)
Theme: Twenty-Twenty One (default)
Other Plugnis = none

Host has upgraded to PHP 8.0 (but s2Member is a fresh install).

Please advise. Thanks.