ever since minecrafr 1.10 or so mouse scrolling in the hotbar has been broken on mac os.
if you want to scrol 1 block inside the hotbar i need to scrol my mouse 10 notches
meanwhile in minecraft 1.7.10 this issue is not present
i first thought it was my macbook but then when i got a new macbook the same issue is still present
see video of both 1.7.10 and 1.14.4
as someone who uses 1 notch scrolling alot this is considered unusable for me.
You should be able to change mousewheel sensitivity in the options.txt file in the minecraft folder.