Okay, this is an odd question, but hear me out:
How do you get rid of the lowest UI button on the left hand inner panel, it’s Xpose.
Normally to get rid of an UI element, you’d go into custom UI, enable mode and drag it to the canvas. Only by enable customize UI mode everything shifts down not allowing you access to the furthest button and you can’t scroll down either.
Answers on a postcard please 
Hello!
Note that the recommended specs for Zbrush specify a display of 1920x1080 or larger.
You can scroll the buttons in that slot by finding an empty space in that row, and ctrl-dragging on it. This will let you slide the button back onto the screen.
If you’d like to fit more buttons on screen without having to do this every time, the button size, which is actually a UI scaling feature, can be adjusted in Preferences > Interface > UI. Be sure to store the config. the changes will appear on the next startup.
Ctrl + scroll! That’s what I was missing. Thank you!