As one example, I had to take a proctored exam recently, and the only supported OS was Windows or MacOS. Linux was not an option.
Then there is games, Proton is great but plenty of AAA titles are still not compatible.
Just for starters.
Got on the phone with support and they were dumbfounded. Got the idea to just spoof my user agent as a windows box on edge and it worked perfectly afterwards.
Even if not done on purpose there is a lot of crufty shit online that breaks in unsuspecting ways when I'm on a linux/BSD box. Especially if interfacing with the government websites and webapps. Our state fire code website looks straight out of 2002 and has multiple warnings about making sure to use IE6... in 2023.
Maybe its just my use case (fire industry / local government), but it helps to have a mac or windows machine lying around as backup.