Planet Zoo is a beautiful game, and you will probably want to capture a few screenshots at certain points in the game. The UI is not really that beautiful though, so you might want to hide it away while you press Print Screen or F12 if you are playing on Steam.
Luckily for us, it's very easy to hide the entire UI in Planet Zoo. All you need to do is to press G to hide the entire UI/HUD. This will obviously make it very difficult to play, but at least you are now able to grab that beautiful screenshot without any clutter.
To get the UI back again, press G once more and it will return. You can change the keybinding for hiding and restoring the UI by going to the key bindings option, but G will be the default key if you haven't changed it.
And that's all there is to know about hiding the UI/GUI in Planet Zoo.