Valve are pushing out updates rather often to the Steam client lately, with the fourth this month now out.
On top of removing Steam Play options for Mac and Windows, along with a Steam Input bug fix we also saw these updated to the Steam Play integration on Linux:
- Fixed an issue with invalid Steam Play tool selections if user had previously opted in to enable Steam Play for all titles. (Note: this will cause a one-time reset of all Steam Play global and per-app selections to the default state).
- Added the ability to force Steam Play compatibility tools for non-Steam game shortcuts
Nice to see the ability added for shortcuts, for games from other sources you add into Steam. Could be pretty handy.
Note: Apparently there's an issue where it can remove your Steam Play games and redownload them. A fix is to set Steam to use Steam Play for all titles and restart the client as soon as possible after updating. You can also try it in offline mode, to prevent any downloads.
See the announcement here.