I rolled back to a working backup VM of Rawhide Budgie and selectively upgraded until I could no longer log into a Budgie session, and it's the upgrade to gnome-session-46-alpha-1 that did it. Previous 45.0-6 works.
Further, downgrading gnome-session to 45.0-6 on an already broken system has restored it to a working condition.
Yes, this is known. We created budgie-session and with it approved, I can land it in Fedora and update Budgie to the latest release. gnome-session isn't going to be used at that point.
Metadata Update from @joshstrobl: - Issue status updated to: Closed (was: Open)