I followed the webpage https://docs.percona.com/postgresql/15/apt.html which gives instructions how to install Percona Distribution for PostgreSQL on Debian and Ubuntu.

There is one Hint there on that page suggesting:

You can connect to psql as the postgres user in one go:

That didn't seem to work on my Ubuntu 22.

I think the correct command should be this:

Note the -c option makes the difference. According to the man page of su:

But if you want to eliminate all error messages, I'd suggest to modify the command like this:

Note the additional - after su. See: https://unix.stackexchange.com/a/460769 for more information.