Don’t know what this knot is called, but it’s all I use

I think it's called a surgeon's loop topped with a square knot. I use this with circle hooks, obviously. But also flouro leader-to-swivel, braid to swivel, braid to popping cork, etc. It's really the only knot that I ever use.

(Note – I almost exclusively use a Carolina rig with live bait, except when I'm using a popping cork with a 3' leader under it for with live bait.)