I’ve just migrated from a Mac running OO Pro (current version) on Mojave, to an M1 Air running Big Sur, and QuickLook seems to have stopped working for OO (and OmniGraffle, by the way). Actually it seems to have stopped working in two different ways: some OO docs have a file icon, and some have a thumbnail view of the doc as their icon. In both cases, this is all that QuickLook shows.
I’ve tried rebuilding the LaunchServices db - no change. As far as I can see, no other file types are affected.