If that really meets my needs, that will pull me away from KDE to a wlroots based compositor. I'll try it later, thanks.

KRDP: https://invent.kde.org/plasma/krdp

But it needs a logged-in session, you can't get access to the login manager.

I want to connect to a logged-in session; I can't get krdp to let me do it without me locally granting permissions though.

They fixed that. I can definitely connect remotely in an unattended way as long as I'm logged in locally.

These might have something to do with it:

https://develop.kde.org/docs/administration/portal-permissio...

https://invent.kde.org/plasma/krdp/-/merge_requests/102

wayvnc works for wlroots-based Wayland compositors, sadly not all Wayland compositors are wlroots-based

Well, yes, the answer to basically any "can I do foo in Wayland" is "as long as you're on compositor bar or baz" because it was built in a way that guarantees fragmentation. There isn't a single way to take a screenshot, of course remote desktop is fragmented. But wayvnc is a good answer to the question, even including that caveat.