BUG #19378: How do you know to start Postgresql with "systemctl start postgresql@18-main" ?

The following bug has been logged on the website:

Bug reference: 19378
Logged by: John Radley
Email address: jradxl2(at)gmail(dot)com
PostgreSQL version: 18.1
Operating system: Ubuntu 24.04
Description:

If a beginner comes to Postgresql 18 for the first time, without any
previous knowledge, and follows your instructions to add the Apt Repository,
and then to install version 18 with the command, "sudo apt install
postgresql-18"...

How do I know I should start Postgresql with "systemctl start
postgresql(at)18-main"?
Even then, it doesn't start as there is no default,
"/etc/postgresql/18/main"

I don't see anything about this in a FAQ.

All it takes in your documentation (see below) to mention,
"You can check the database is running with, systemctl status
postgresql(at)18-main"
to give the User a clue.

I'm sticking with Ubuntu/Debian's v16 packages... At least it works out of
the box!

Ref:
https://wiki.postgresql.org/wiki/Apt
https://www.postgresql.org/download/linux/ubuntu/