I have a site with login problems.
Using sitename/wp-login.php gives me an error message > critical error
Using sitename/wp-admin.php works better, I get logged in, but there is still an error message about a missing page, but not which missing page…
I got an advice to go back to PHP 7.4 but that dis not solve the problem.
So Im having the same problem in 7.4 and 8.0