Hello,
I did a very similar injury 12 months ago, ruptured ACL, PCL and MCL in a trampolining incident...
Had the ACL repaired and MCL stapled and cartilage removed.
PCL couldnt be repaired for same reason.
I did try a few searches at the time to see what I could and couldnt do but difficult to find much.
I find I loose control when the knee is weightbaring and flexed more than 90 deg (like the squat you mentioned). I can feel the shearing in this position so even things like going down a steep step etc has taken me over a year to achieve. Other than that I was told (apart from contact sports) I shouldnt be restricted from doing anything. I also feel shearing when changing direction. PCL limits tibial rotation also, I find I still feel a clunk when changing direction quickly or without thought.
Hope this helps
Phunphysio