ElTerprise: I explicitly left out the Interplay mentions (for the most part) because the situation is not that clear. Some mentioned have Mac/Linux builds. I need more information, are these more recent builds, or what's the difference?
I think either some of those Mac/Linux ports might have already been on GOG but not on Steam at the time of
the tweet or they were added some time between the tweet and today. I checked SteamDB and ALL of the games mentioned have both Mac and Linux builds on Steam. The situation with GOG is a bit more complicated (according to the store pages):
Conquest of the New World: Missing Mac/Linux build
Cyberia 2: Resurrection: Missing Mac build
Descent: Missing Linux build
Descent 2: Missing Mac/Linux build
Dragon Wars: Missing Mac build
Earthworm Jim 1+2: The Whole Can 'O Worms: Missing Mac build
Kingdom: The Far Reaches: Missing Mac/Linux build
Lost Eden: Missing Mac build
M.A.X. + M.A.X. 2: Missing Linux build
Prehistorik 1+2: Missing Mac build
Redneck Rampage Collection: Missing Linux build
Screamer: Missing Linux build
Screamer 2: Missing Linux build
Shattered Steel: Missing Mac/Linux build
Stonekeep: Missing Mac/Linux build
Subwar 2050 Complete: Missing Linux build
So I have no idea whether the Mac/Linux builds on Steam are newer, but it's clear that GOG doesn't have some of them at all.
Lucian_Galca: Are we sure about Cardaclysm being on the list for missing updates? The list notes say it's missing updates since March, but gogdb says it's updated well past that and the last posted changelog on Steam
You're right, according to GOGDB, the last two updates were on 9 March 2021 and on 26 July 2021. Last update on Steam was on 22 July 2021. I think the game might be up-to-date. It was probably reported some time after the last March update and then nobody noticed that the game was updated again in July.