I think you're looking for the `toggle_split_zoom` binding which has existed since Ghostty 1.0 and is default bound to `cmd+shift+enter` on macOS which is the same binding as iTerm. It's also visible in the menu and command palette.
We recently added a kind of split title bar, making it double click to zoom is a good idea. I'll add an issue for that to the roadmap.
1. The quick terminal feature is ghostty's killer feature for me, I switched to ghostty because of it. Could we make it first-class feature? Like, i'd love to have tabs over there too (like in guake/yakuake).
2. I have a white on black theme (white text on black background) but when i split vertically/horizontally, the borders between one shell and the next are not really visible and I have an hard time resizing them... Can you do something about it? Setting the colors of borders would be an okay fix for me.
Just FYI, it's in Kitty nowadays too: https://sw.kovidgoyal.net/kitty/kittens/quick-access-termina.... The quick-access terminal is a regular terminal, so you get normal tabs, splits, etc. there.