alr, while doing GUI’s, etc I have one problem I do not know how to hide it… I know there used to be a button to hide it and I do not know whether it has been moved or just removed altogether. (In-studio not an in-game button)
Anybody know whats going on?
Once you are in Roblox Studio, click on the view tab and you will find the UI Visibility button next to the switch windows icon.
You could also change the property ShowDevelopmentGui of StarterGui, this does the same thing
Thank you! I will make sure to try this out. 
Thank you! If the other comment doesn’t work I will try this out.
As stated by RemainingTissue, you go to View > UI Visibility to toggle it.
Or if you still wish to use something similar to the old hide UI button, you could use this plugin that mimics it:
https://create.roblox.com/marketplace/asset/10775022880/Legacy-Ui-Toggle
Cheers.
