You have to set to trust from peer the first time you download and install postgres.
Because there is no default password.
After you create a password.
Then you can reset from trust.
If you have sufficient access to do this you can just login using the existing peer connection and change the password. No configuration file changes are required nor recommended.
You also have to reboot your computer each time you change etc/postgresql/12/main/pg_hba.conf.
at the very least restart the database.
Hardly. Reloading configuration files on the fly is a thing. The documentation describes how to do it.
