Are you sue you are using iTerm? Any way I'll sugest to forget about it and use Terminal, for a macOS experience. iTerm remembers me of Linux, you have all the options but you'll spend all day configuring it and when finally is ok then some bug will hit and take your peace of mind How to exit alternate screen scrolling on iTerm2 Vim?.
This might help https://apple.stackexchange.com/questions/6504/how-do-split-panes-in-terminal-work. And @BennyPowers answer at https://superuser.com/questions/55459/how-to-get-vertical-split-of-terminal-in-mac-to-execute-different-actions.
I use the macOS native way to split vertically and GNU Screen (which came with macOS) to split horizontally. Execute screen
then C-a S
(to split into two regions), C-a TAB
(to swith to the other region) and C-a c
(to open bash).
You can even resize it with C-a :
then type resize 10
i.e. and for more man screen
.
When its done you exit
andC-a k
to destroy the window.
For completeness. A lot of people say tmux https://github.com/tmux/tmux/wiki is a better alternative to GNU Screen. I never tried afraid of the same experience I had with iTerm 2.