phaolo: for example, offline achievs could be marked differently or kept private, whilst only online\valid ones would be public.
I think the problem is the "do not allow offline achievements" or flagging them differently the first poster suggested doesn't even solve the cheating problem as it falsely believe that using SAM offline is the only way of unfairly unlocking achievements by blocking primitive detection methods like Steam / Galaxy watching for achievements that are unlocked without the game even running. In reality, I can think of several other ways of cheating achievements by manipulating in-game mechanics without ever using SAM all whilst running them "online" via Galaxy / Steam. Eg:-
- A trainer / Cheat Engine that increases your movement speed, ammo, health, gifts items, slows down time, etc that makes it 10x easier to unlock from within the game without tampering the achievement directly from outside of it.
- Start a game online, save, quit, use a save game editor, then continue online. Or using someone else's save game files. If you blocked the latter, then you'd also be blocking the ability to locally back up and restore your own real saves for future reinstalls.
- For some engines like Unreal, simply using the engine-level hidden developer cheats. Eg, for Bioshock 1-2, edit the User.ini config file, find the keybindings and add the lines NumPad1=God, NumPad2=ghost, NumPad3=StopSecurityAlarm, Numpad4=GiveItem 1000 ShockGame.ADAM, etc, to enable in-game God Mode, no clipping, free items, instant alarm disable, etc. Other engines have similar in-game "hidden" console cheats / "developer mode" that really aren't that hard to find.
- Mods. Many games don't specifically exclude them for achievement related stuff.
- Other stuff. Eg, if a horror game achievement is hard to get because the area is too dark, use your AMD / nVidia GPU driver or SweetFX to simply increase the gamma.
Any achievement segregation / annulment based on a very naive
"playing offline = possibly cheating, playing online = guaranteed not cheating" just gives a massively false sense of security whilst the cheaters are openly laughing at those who think "SAM" is only way of cheating achievements. The only way around this stuff (and much more) is to require all games (inc single player) to be played only online and include Server Side Cheat Detection (such as FairFight as used in PUBG, Fortnite, etc) that constantly monitors every metric in the game from remote servers. But then what the OP ends up arguing for (without realising it) is demanding GOG introduce DRM into GOG's DRM-Free games...