How can I have the dock centre screen with a keystroke reveal/hide

It's probably a third-party app which no doubt doesn't work anymore because dock hacks have to work at the system level or SIP has to be disabled.

You don't need an application for this with command+Tab.

This isn't the Dock, but the App switcher you see when you type cmd-tab.

That is NOT the Dock.

It is called Application Switcher - and easily accessible with Command-Tab.

is there a way to change the HUD size? It's huge on my screen.

I don't know any way of directly manipulating its size. It does adjust automatically depending on the number of open applications - so if you have many open applications the icons appear smaller so they can all fit, and so the hud itself becomes shorter in height.

It should not be of any concern, though, as it is something that does not stay permanently on screen or cover anything.

Actually I forgot all about App switcher since I use the keyboard as little as possible. 😮

But, on a 27" screen, when I opened it with only 2 apps running, it scared me it was so large. 🙂

I'm sure I won't see it again for a long time. 😎

fwiw, there is a shortcut to show and hide the dock. the problem is it doesn't prevent the dock from showing if you move near the bottom of the screen.

While it won't show in the middle of the screen, you can set a shortcut to "Move focus to the Dock." The Dock will show where it is pinned and you can use the arrow keys or type letters to select an item in the Dock.

Keyboard System Preferences, Shortcuts, Keyboard.

But, if all you want is to hide and show the Dock, dialabrain already suggested that.