I want to make animations for my player but for some reason I can't, It has a proper rig, in the muscles and settings tab it works fine when I try to move it's muscle groups. It also has Animation and Animator components on it. When I go to the animation window and when I press the record button the bottom part of my player disappears/folds in half , and rotates to the left, here are some screenshots: https://imgur.com/a/PMXCgqT

I don't really know too much about 3d so all I can do is recommend watching tutorials online. Maybe brackeys. Also you post on unity website or stack overflow to get better results.

Under the Rig tab, are you using generic or humanoid type animation?  Are you using root motion?  Is your avatar definition  set to 'create from this model'?  Are you using a blend tree?  I would just triple check those model settings in the inspector to see where the weirdness is happening.