I'm thoroughly confused. How can a full screen program allow for a side by side?

Full screen is a mode that takes away the ability to move windows, and removes their chrome. You can have two windows in this mode, and they will just take up the whole screen between them.

I get a bunch of ui issues doing full screen, and though I use Magnet for snapping, I want something that stays snapped. Looks like this will do it.

The maximize button has an option to go into a split screen mode where you get two "half full" screens (i.e. side by side but still hide the menu bar, window chrome).

I wish there was a keyboard shortcut to run apps full screen