For some reason the Visible function in my Powerapps won't work I just wrote in OnSelect() Mail.Visible = false
The Mail is in this case a Textinput/ TextBox.
When I click on the button nothing happens. I can't find a documentation about it on the MS Website but I have in Powerapps a fuction called "Visible"
Credit @SeaDude
This worked perfectly for me toggling the variable back and forth to show/hide a few layers.
Set(mailVisible, !mailVisible)