Best solution: Upgrade everyone to scram, then change md5 to scram in pg_hba.conf and never look back.
To expand more on the "upgrade everyone to scram", that means force all users to set a new password while using scram (which should be the default). You can do it yourself by getting a list of users and changing their passwords inside psql:
-- List all users still stuck in md5-land:
greg=# select rolname from pg_authid where rolpassword ~ '^md5'
alice
eve
mallory
(3 rows)
-- Just in case, force use of scram
greg=# set password_encryption = 'scram-sha-256';
SET
-- Reset each user's password to some strong password of your choice:
greg=# \password alice
Enter new password for user "alice": Enter it again:
-- Repeat the above until this query returns no rows:
select rolname from pg_authid where rolpassword ~ '^md5'
