Editing a staff is not possible with one instrument
When trying to edit a staff, it doesn't seem I can do it as described in the documentation. Reading https://musescore.org/en/handbook/3/tablature#by-changing-staff-type I see:
"Right-click on the staff and select Staff/Part Properties…"
But in practice this option is only available if I click on the instrument's name. That option does not come up when I right-click on any other area. When there's only one instrument, the name is not displayed, so the option doesn't seem reachable at all.