Many problems after Catalina install

Hi, since installing Catalina over a week ago I've had many many problems that have rendered my Mac Mini pretty much unusable.

1. Apps constantly verifying several times (i.e. Affinity Photo)
2. Trash will not empty (shows emptying trash progress bar until I restart Finder)
3. Apps will not launch (bounce in the dock for ages then do nothing)
4. Mac running generally very slow (as if its doing something constanty in the background)

Things I've tried:

1. Booting into safe mode
2. Running Disk utility
3. Performing daily/weekly/monthly scripts
4. Clearing startup items
5. Creating a new profile

Nothing has worked. Can anyone help please?