Error: The MAC is invalid

Just to clarify, the issue is not with user passwords.
It's with service credentials, and lookups.
These values are encrypted using your .env's app key as the key. If this key changes, the system can't read the credentials stored in the db, and it locks up.
Go into the tables for your SERVICES (not users) and set the credentials all to NULL.) You will need to know the actual credentials so that you can set them correctly in the admin app once everything is back up and running.
Do the same thing for lookups. Those values are also encrypted.