I periodically check to see if my phone has been adding apps when it self updates.
Today I learned that the TikTock app is almost a Gig. I have never used it and don't recall adding it.
Buhbye ticktock hello free space.
Hopefully things run better now
I think if you have a FB account, you kind of have a default IG account? I am not sure, but I know what you mean because I get the same thing.