Ways to extract the files isn't actually the same as a portable install though. A game that normally makes registry entries may still work if they're not created during installation, but it will create them when it's run in that case, and still leave them dangling when the files are deleted. And it'll still put the saves wherever the heck it wants. An actual portable install must store all its data in the game folder.

It's like nobody--even among veteran Goggers--actually looks at where any of their games write save & config data to, and, therefore, just assumes that this data is actually being deleted when they uninstall the game.

I cannot afford such ignorance, since I backup all the saves of all the games I play, once finished.

AFAIK, GOG uninstallers never delete saves outside the game directory. Which isn't too surprising as I am certain they have no knowledge of where these saves are located (nor should they, IMO).

I have a script that backs things up daily and include game saves in it so definitely need to know the location as soon as I start playing a game.

But quite sure that the uninstallers do delete those folders too if you tell them to, at least usually. And they also tend to create them during installation, so they know where they are.

I have never seen either of these occurrences for non-emulated (i.e. non-dosbox, etc.) games.

Can you point me to a non-emulated game for which (a) the GOG installer creates a save directory outside the game directory, or (b) the GOG uninstaller deletes a save directory outside the game directory?

Tested one game just now (Cramped Room of Death):
- install did not create the save directory (launching the game did, in AppData\LocalLow)
- uninstall did not delete the save directory (regardless of option chosen)

Hm, was sure that it did. Then again, with how rarely I install or uninstall a game (see how rarely I finish a game) and how much of an automatic reaction cleaning up after uninstalling is, I may not even remember that I'm doing it each time.

Well on Linux if you install each game into a separate WINE prefix you actually can just delete the folder to clear everything since the prefix folder contains the entire Windows directory structure used to run the game.

I was never a fan of programs placing files outside of their install directory. Particularly games. I think multi-user PCs with multiple people gaming on them are rare enough that it would be fine to just place everything in the game folder. Save games are not sensitive information.

And if you live with someone who games on your PC that is malicious you likely have more pressing problems.