I started daily driving linux in the 90s. When I switched to a mac around 2010 if found Mac exhausting. It had different usage patterns than I was used to. Some of my most used features weren't there. Having a reasonably usable shell experience required lots of tweaking and macports then brew. When I switched back to linux ~5 years ago there was a while where getting back into the linux groove was exhausting because I wasn't used to it, but not as exhausting as switching to mac because I already knew it, just needed to get back in practice.
Every time i use windows (which is rarely, once a year maybe) i find it exhausting.
I propose that it's not the OS that's the exhausting part - it's the switching to a new environment with different workflows and thought processes around it that is exhausting. Similar to how it's much harder to get familiar with a codebase in a new (to you) language than in a language you are proficient in - but both cases can be taxing.