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