BTW. Did you contact support about this?

A lot of your complaints are rooted in GOG trying to sell new release games, which I do agree they fumble the ball with a lot of the time. They're trying to walk a line between people who see any kind of client or what-have-you as inherently evil and people who want the newest features on the same day Steam gets them. It's a rock and a hard place situation if you ask me.

If you stick to using GOG as an old games store and buy stuff with the old installers and no complications then it still works just as well as it ever did, in my experience. When I buy something recent here, like say PoE2: Deadfire, I sometimes have minor regrets but I try to keep in mind I wanted to make a statement about DRM, as pointless as it probably is at this point.

As I said, there's enough to complain about here, and actually a lot of things on that list Steam does actually better (so your GOG == Steam is invalidated en passant).

But the topic at hand is telemetry built into the game engine, and that's something that GOG has no ruling over (other than deciding to not sell Unity games... imagine the outcry). Which may be considered Spyware (MS/Win 10 really broke the dam here, I guess...), but isn't DRM.

I don't want to belittle the problem, games (or all applications at that) using telemetry should at least nicely ask before sending any data. But blaming GOG here is like blaming you local electronics store for selling Amazon Echo.

I take it you've seen the responses in this post on Paradox's own forums?:-
https://forum.paradoxplaza.com/forum/index.php?threads/game-keeps-phoning-home.1096956

I agree with the poster who wrote this:-

"In that case it probably just had an issue with timing out while trying to determine if it was online or offline. Like maybe it's not even really trying to send anything, just determine if it is online or not so it can decide if it should be sending achievements to galaxy or whatever. That would make sense even for the non-galaxy install, since it would still need to check if galaxy was running and in online or offline mode. It's maybe not the best implementation, but it makes sense. The person who wrote the code didn't account for the indeterminate state, assuming the packet would quickly be responded to either as a ping or a rejection notice."

It might be worth doing a summary Crash / No Crash "test result" post like:-

Firewall disabled = No Crash
Firewall enabled, asks user for permission = Crash
Firewall enabled, auto-block outbound by default rule = No Crash?
Firewall disabled + Network cable unplugged / Wi-Fi disconnected = ?
Firewall disabled + Network adaptor disabled in Device Manager = ?
etc.

It might help the devs / GOG narrow down the issue. Eg, it's highly unlikely the Windows Firewall is bugged given it works fine with every other game, but it's possible the network access detection code in the game / Galaxy.dll may be buggy if it expects an instant success / failure network access response, whilst the Firewall instead gives no response whilst waiting for user input and that delay is what's causing it to crash? I don't know if it is that, just throwing ideas out there. It definitely needs sorting though.

Overlooked that part... kind of beats me though why a game would use Galaxy functions to "phone home".

okay that sounds a bit better aas it indeed confirms the game works offline

Example "Witcher 3":

No Galaxy installed.
Game tries to connect to 46.105.121.139 (galaxy-log.gog.com)

Complete block by firewall: CRASH
Allow local loopback, block all other connections: NO CRASH

The problem is the galaxy.dll. I made a dummy for this dll and the game worked without trying to phone home.
I have this weird problem with many GOG-games. It really needs a fix.

A couple of questions as I have a few games that do this.

Firstly, how do you allow local loopback, I have 127.0.0.1 galaxy-log.gog.com and 127.0.0.1 in my host file but the game(s) still crash. I feel I'm missing something but I really don't know what.

Secondly, how do I make a dummy galaxy.dll? This sounds like a good workaround.

Thanks in advance.

[emphasis added]

Please give the last bit in the OP (right after the one you quoted in your post #37) another read - Killjoy_Cutter indirectly says that they don't even have the client installed. They stated it more clearly here (installed the game using the classic standalone installer).

This isn't the only game that behaves this way, and this behaviour has been a topic of discussion going for a couple of years (for just a couple of examples, follow the links given in this thread, and especially Geralt_of_Rivia linked post; it's 2yrs old, but still current) - a recent one in the German announcement thread of profiles, where user Cattie provided some unsettling info.
So yes, please fix this problem.

Er... hold on a minute, GOG is now using Amazon AWS for its servers? I really hope this is some kind of misunderstanding, because AWS's ToS makes it explicit using their servers gives Amazon unlimited access to any information being used in the process.

No, it's the Unity engine's telemetry. Read my previous post.