Have you tried the "nuke from orbit" approach of a full system wipe (T2, SMC and NVRAM reset, delete recovery partitions, Pre-boot volume, etc) and doing a fresh install and setup rather than restoring from backup?

I know it shouldn't be needed but sometimes it is the only option.

It isn't much help to you but my experience with Catalina has been very positive on a 2018 15" MacBook Pro. The initial release and first two point updates had some silly UI bugs but since .4 it has been solid as a rock for me.

I just updated to .5 and noticed I haven't had to restart my laptop since the last update I installed 42 days ago. In those 42 days I haven't had a single issue so I am pretty happy about that.