This is more complicated than I thought.It turns out that the flameshot that gets launched on startup in Waldn if I have it configured to do that doesn't work, but if I close and relaunch flameshot from the terminal it is able to capture screenshots.
So the problem seems to be that flameshot processes that aren't launched interactively don't work properly under Wayland.
I've posted about this at https://github.com/flameshot-org/flameshot/issues/3326 .
