Following on from the kernel regression discovered yesterday, this appears to be a regression with FUSE that can be triggered by Flatpak, it's still unclear if Flatpak is the only trigger and going by other reports I'm assuming it's not.
There are a lot of tools that rely on FUSE functioning correctly but at least the problem is known https://gitlab.archlinux.org/archlinux/packaging/packages/linux/-/issues/110#note_243523