Focus-follows-mouse, even sloppy, is problematic on macOS due to the menu bar. Moving the mouse up to the menu bar means covering space which can belong to a different window, which would change the meaning of the menu item when you got there.
"Focus-follows-mouse, even sloppy, is problematic on macOS due to the menu bar. Moving the mouse up to the menu bar means covering space which can belong to a different window, which would change the meaning of the menu item when you got there."
This is true, but easily surmountable.
Mondomouse, which is the last bona-fide focus-follows-mouse add-on that existed for OSX (circa snow leopard) had a switch timer that was user-definable.
So you could set the switch timer to .5 seconds or 1 second or something which would allow you to run the mouse across other windows without changing focus. That solved the menu bar problem that you are, correctly, pointing out.
I think it's also worth mentioning that if you're at the point where you're demanding FFM, you're probably already doing everything with hotkeys anyway so it's not like you're running up to the menu bar often ...
Focus-follows-mouse is sorely needed, at least as an option, in OSX.
I used to achieve FFM, circa snow-leopard, with the excellent "mondomouse" from AtomicBird, but it is no longer maintained and will not work with modern OSX versions.
Looking ahead, it appears that there is some new capability buried deep inside the accessibility section of Preferences that actually enables FFM, but I do not have a new enough (Mojave ?) version of OSX to verify this ...
EDIT: I think it is actually High Sierra that this new accessibility feature appeared in, but again, not sure ...
Highlight-to-copy works inside the Terminal app, it just doesn't use the public pasteboard. You Shift-Command-V to paste. Dunno whether MMB would work too, or could be configured to do it.
yabai has a feature that allows for focus following mouse. It's a little wonky with the menu bar, but it works pretty well and replicates the X11 feel pretty well.