MacOS has a built in 4x4 window tiling which works for this purpose for me. I don’t find ever wanting more than 4 windows open on an ultrawide. Definitely not as powerful as something like xmonad but useful for the majority of my use cases.
You can, I believe, but I often need to move between computers so I try not to mess with shortcuts too much (or go down keyboard layout rabbit holes, etc).
Browsers only ever get maximized to the left/right half screen for me too
Which is something macos should really improve on though, the ux is pretty bad compared to Windows and Linux there