Store page says:

Why buy on GOG.com?
DRM FREE. No activation or online connection required to play.

Overall most helpful review says:

The game is nice and fun and definitely worth its money, but since the Developer was bought by Paradox Interactive you are required to be connected to the internet when starting the game, because you have to launch through the Paradox Launcher ( Third-Party-DRM, so much for the Advertised 'DRM-FREE'nes)

Is this true? If i want version with DRM i'll just play my already owned steam one...

Apparently the paradox launcher will be installed alongside the actual game but it's really only needed for multiplayer functionality. If you're just in for the singleplayer it can be ignored completely and won't even start when running the game from the main executable.

A couple quotes from https://www.gog.com/forum/general/the_what_did_just_update_thread :

"I just tried, installed the game, never had the PDX launcher before. Game booted just fine.
Sure, it installs the launcher, but you don't need an account and it works offline perfectly so, eh?"

"Just tested it myself. If you start via executable the laucher will not even be started. It will only be started if you use the GOG shortcut or execute it by yourself. That is of cause important just for those who absolutely despite the launcher since - like omega said - it's optional to log in."

"What happens if you start from Galaxy?"
"Just did a fresh install of Prison Architect via Galaxy and it does start the PDX launcher, but you can just hit "skip" in the upper right corner (see attached picture) and play without using an account."

Thank you for the information, that is good to know,

Does that mean I can remove the launcher once the game is installed and still play it just fine? I don't care about MP and would rather not keep unnecessary software around on my computer.

You can uninstall the 'Parasite launcher" in Apps, but if you launch the game afterwards from GOG Galaxy, it will reinstall.
Running from executables works, but you won't get Achievements, time played tracking or any feature in galaxy for this game. Which.. is a bummer.

The Paradox Launcher DRM also reinstalls itself if you click the "Launch Prison Architect" shortcut...

Why this is discussed in an old thread - as the conditions changed two times since this thread:
* https://www.gog.com/forum/prison_architect/extreme_nasty_drm
as the launcher was no longer used about March 2020 and after a few years was reimplemented
in an even nastier form than before: now even installing further launchers without asking.

So you can use Prison Architect without the internet - but you have to edit start.sh or invoking the right binary.

Such launchers and spying DRM may be normal under Windows, but this is unheard of under GNU/Linux.
So this is not only DRM - it is really nasty DRM - and should not be in accordance with EU law AFAIK.

But you can circumvent it by technical skill - if you know that there is a bomb waiting to get defused.

And yes, I had written a good review that it has no DRM as the launcher vanished from Prison Architect ...
so I don't like to get fooled with such bad purposes.

Additionally there are better games of this genre in GOG which don't need to use DRM at all!
So it IS the gamers choice!

I have to disagree with the comment from "vine01": my game-time is still tracked, with a Custom EXE, and I've had an achievement within the previous six months of posting this.
It has to reapplied after every update, but it is easy.

However: please see the comment from "JMB9" in this thread as to how and why this (also) may not matter...

is it correct that prison architect now comes with that parasite launcher?
if correct, is there a way avoiding installation of that paradox malware?
or do i need a pirated copy in order to play game i bought back in 2016?