Same here, I think this is probably related, weirdly for me it sometimes defaults back to OneUI but in the default apps list there is nothing selected. It just deselects the customer launcher sometimes after a reboot.
Personally I like samsung gestures more, swipe and hold is just too slow. but I like the swipe pill to move to recent apps, it works with both samsung and android 11 gesture system problem is you need to keep them visible and i can't stand those 3 pills at the bottom even with good lock mod navstar.
How did you disable launcher activity only? in app manager I'm only able to disable entire one ui home, can't disable individual activity .