Can i use MySQL 8 or does it have to be 5.7
https://community.socialengine.com/forums/topic/2307/mysql-8-0-compatibility based on that it works. We also use it on our stagings and it seems to work for us. Please note that you did not state your version of SEPHP. We are working with v6.2.2.
I have been using MySQL 8.0 since about April 2020 without problems, except that
for SocialEngine, I find I have to use shorter database user passwords (about 32 characters. I prefer much longer); and I needed to use mysql_native_password rather than SHA2, although that may have been a PHP 7.2 compatibility problem.
If you have problems getting Social Engine to connect to the database, run the following line of SQL as the root user, substitution your own username and password:
ALTER USER 'username-here'@'localhost' IDENTIFIED WITH mysql_native_password BY 'password-here';