Knights of Spamalot
What unattached instances should I be looking for if I wanted to do the same?
Often, they all can't be removed, depends how well you prep and pick the save to narrow it down.
If you remove something that shouldn't your game likely will fail to start / load.
To specifically answer your question it is trial and error.
I go to an internal cell away from any settlement and wait, save and then see if you have any.
hopefully, it looks like this:
If what I circled has unattached instances then you might want to clean.
Without getting long winded "here you may need to repeat for each or clean them all" then go back in-game and see if the save loads. I have no idea what mods you may have uninstalled therefore can't tell you what to look for. "What unattached instances should I be looking for if I wanted to do the same?"
You should seldom if ever have to do this if you are practicing good mod discipline but if it is needed the below is how you do it.
Pay attention to GA_'s instructions in the section: For Your safety and Peace of Mind
Here the guide:
5) FallrimTools Guide (ReSaver)
Good luck Quad. It is a good tool but as-is it is a fallback and not a perfect substitute for mod discipline.
Hopefully, this helps a bit.