Hi,
sorry about the problems. The upgrading docs for 14.5.0 mention a background migration for MR diffs which might take longer.
Though, the error message with changing the user name looks like a bug or a missing config update for pg_hba.conf. Can you open a new bug report please?
Please also share which PostgreSQL version you using 
I’ve found a possible workaround when googling for the error message, maybe Gitlab-ce docker on apple m1 stuck on Recipe: gitlab::database_migrations - #13 by joe-huersch helps?
Cheers,
Michael