The way id did it was (because they had Linux guys as part of the company) to make a Linux version, and make it work, but not officially support it if something went wrong. When Bethesda bought them they weren't interested in unofficial releases and they weren't interested in providing official support.
The other part is the source releases: after a game engine had been out for a while id would release the source code for the engine so that people could play around with it and port it to other platforms. That's why Quake 2 RTX can exist now. Carmack had it as part of his contract when Bethesda bought id that they'd release the source to the game they were working on at the time, but they weren't interested in doing the same for future releases.
Bethesda just have no interest in releasing games for Linux, even if they already exist internally, and even if they've been released on Stadia (which is Linux). More market share or a change in management might change their attitude, but I wouldn't hold my breath.
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