Rectangle is so good - it's the first thing I recommend anyone new to MacOS download. I don't know why apple hasn't implemented this natively.

Magnet is also pretty good

Hammerspoon is by far the best option for devs, it’s more powerful than pretty much every solution out there, including better touch tool, and the only additional software I need is karabiner elements and alttab. Those three pieces of software will solve every single problem you have with Mac.

Does Rectangle has a shortcut to switch the focused window in a split screen?

No but Amethyst does

https://github.com/ianyh/Amethyst

Hammerspoon can do it for I have it in my config. I also have it so I can switch to open windows on the same Space (I can throw windows into a tiled view and jump around to them). It's extremely flexible if you are willing to play around with it.

I’ve kind of solved this. You can snap windows but you need to add a shortcut in systems to do it. It’s not perfect, but it does work and overtime you miss it less and less

I’m a very happy user of Rectangle, as well.