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Cyril79: Seriously I don't think they intend to release the Linux/MacOS builds on GOG now.
Another one bites the dust?
shmerl: Something is off clearly. I asked their community manager about it, and she only said they have no ETA.

But that's 2 months and a half, it doesn't smell good IMO.
This reminds me of many other missing Linux releases on GOG... and I don't like that.
So, really, where is the Linux version given that it exists and is available via Steam? Same with macOS.

Is GOG release intentionally Windows-only?
coming soon at play'it:
wait and see.
I don't think developers care anymore about GOG users.
For what it’s worth, the Steam version of Steel Rats is currently temporarily free to keep (giveaway), and it includes Linux and macOS versions.