Could be plain old hypermobility. My knees will bend kind of like that if I'm leaning against something and not being particularly careful to make sure I'm standing in a "normal" posture.

Bro’s got his entire shaft across the desk

Would be hard to tell without a view from the front. Could be anything from hyper mobility, femoral retro version, tibial torsion, or mix of a few of them.

genetics probably. My feet naturally rotate and touch the ground when I sit. I got it from my grandad who used to call it "duck feet"

i can do 180° with no pain

this is as far as I can go

I got some of the hypermobility genes, but my sister got more. She can do a full split without practicing in years