I think it's okay to break 3rd-party themes if we have a fallback to
Breeze, or some other known-working fallback theme like SDDM does. That
would also fix https://bugs.kde.org/show_bug.cgi?id=433054, which seems
important. It doesn't rub me right to have critical screen unlock
functionality
We have an open MR that wants to break the API of kscreenlocker greet:
https://invent.kde.org/plasma/kscreenlocker/-/merge_requests/29
Effectively this would make any LNF package that shipped a custom
screenlocker to break. Currently the proposal just breaks, but I think
we can make it fall back
