Yes… ish. It works when in a window. In regular fullscreen I would first have to un-rotate the portrait monitor at the OS level. (I suppose this could be automated, but so can having the window be maximised and borderless.)

If, unlike me, you’re not running your games in a newfangled Wayland session (a Linux Display Thing that hasn’t quite replaced our previous Display Thing yet) you might be good either way.

There’s also a "Wide" option that makes the playable area somewhat squarish, which makes it less cramped on landscape monitors.