I can't solve this very irritating issue of Emacs being seemingly smaller than the X window (gap at the bottom). Only a problem with the emacsclient. Does anybody know anything about it.

See here https://www.reddit.com/r/emacs/comments/v7r8mg/cannot_maximize_emacs_frame_on_macos_10pixels/

Adding `(setq frame-resize-pixelwise t)` to your `early-init.el` should help. I'm not sure why I had it in my early init and not the regular one, but it probably allows it to affect Emacs even before the first frame gets created.

>(setq frame-resize-pixelwise t) I am honestly embraced it is that easy and simple. Thank you very much

I was having the same problem as OP, and this solved my issue. I just placed the command in the first line of my init.el, and it worked. Thanks!