GRANT SELECT Simply not working

In PostgreSQL, every connection is to a particular database, and nearly everything you run has effect only within that one database. (One exception is that creation of users/roles themselves is global to the entire "cluster", i.e. running Postgres server.)

In the psql commands you show, you are connecting the first time without specifying a database (psql), which connects you to a database named after the current system user, which is postgres. This is shown at the beginning of the psql prompt: postgres=# (the # shows that you are connected as a supersuser).

It is therefore only this database that is being changed by your GRANT statements.

Your second example uses the correct command to connect to a specific database, psql proton, and you can see that the prompt reflects this: proton=> (with the > replacing the #, since you are not connected as a superuser).

So all you need to do is run psql proton as your postgres user, and run your GRANT statements as superuser on that specific database. Your prompt will read proton=# to show you are in the right place.