Better to track down and fix individual problems, or reinstall system?

In the 4 years I have been using Trisquel I have installed much software from outside of Trisquel repos, such as snaps, .deb files downloaded from the internet, installer .sh scripts, etc. I also have several problems in Trisquel currently, such as not being able to automatically install the next major version, occasional glitches in Caja, Jitsi sometimes not working in Abrowser, a segfault in a program I installed from Guix that was working previously, a graphics error message in a program I installed from flathub that was working previously, lots of lag after leaving the system to run overnight, some lag when loading large folders, etc.

It seems plausible that some of these problems could be caused by me downloading software unsupported by Trisquel, so maybe it's not worth trying to fix them, but then, installing software from random websites is a thing many people may want to do, so if Trisquel could be modified to prevent some issues caused by that, then maybe it is worth trying to help do that.

But maybe it would be better to start over and avoid doing things that would lead to problems Trisquel wouldn't consider issues (because they may have been caused by software downloaded outside of Trisquel supported repos). If I did that, how would I know what to avoid doing? Obviously I generally shouldn't be downloading .deb files from the non-Trisquel-supported sites internet, but what about e.g. compiling software from source code? Is there anything else I would need to avoid?