I didn't see a correct response to this, the answer is flarum doesn't use the newer default mysql password encryption. Assuming you have already created a user and a database, and given that user permissions to the database, I was able to fix this by going into my db and doing:
ALTER USER 'flarum_user'@'%' IDENTIFIED WITH mysql_native_password BY 'flarum_user_password';
I discovered this by quickly going into the console of the container before it shutdown after that 60s wait and attempting to connect to my database in terminal
mysql --host=$DB_HOST:$DB_PORT --user=$DB_USER --password=$DB_PASSWORD flarum_database_name
which displayed an error: Authentication plugin 'caching_sha2_password' cannot be loaded: dlopen(/usr/local/mysql/lib/plugin/caching_sha2_password.so, 2): image not found