I don't see why the self-defence needs to be off to create a restore point as it isn't trying to remove and elements of avast, just create copies as required for the restore point.
I also wonder how avast does its own restore point creation on major changes, etc.
Personally I gave up on system restore over 10 years ago and went over to weekly hard disk imaging and that never required me to disable anything for it to do its job.
Since you no longer use it, it's kind of hard to comment on it.
(I also don't create a full image backup just to try out a utility.)
It takes time to create a restore point. Any time that I've forgotten and left the self protection module active,
the time spent to create a restore point when updating to a new version of Avast has been non existent.
When self defense is turned off, the time spent to create the restore point is normal.
A restore point when needed needs to be something you can count on. I therefore turn off the self defense mode
whenever I need the restore point function.
Your computer, your choice. I know this has worked for me and prevented problems with that function that were evident
when the self defense mode was left on.