I am inputting notes where the choir comes in system 2, so system 1 should only contain piano notes. How do I hide the choir in the first system?
In MuseScore 3.6 to get a "Frenched score" (i.e. to hide the empty staves in a system)
Click on "Format" in the menu, and go down down to the "Style" submenu item.
Open the "Score" dialog, then
a) check the "Hide empty staves within systems" checkbox, and
b) uncheck the "Don't hide empty staves in the first system" checkbox.