The thing is, the latest update (v26.22.0) specifically added support for Windows games installed on Linux to have the direct/via itch switch.
/updates/itch-app-collections-and-steam-shortcuts-proton-support
"Additionally, we’ve added support for creating shortcuts that run through Proton within Steam. The end -to-end experience is now fully functional: you can install Windows games on Linux via itch, and then add them to Steam to be launched with Proton. Perfect for those who are using a Steam Deck and may have picked up a few bundles over the years."
Before this update, I would have been willing to say that this is a missing feature that I would like added -- now, it seems more like a bug.
Are you also on the latest update?
