How can I make a single-line stave that allows three different pitches

You wrote:
Can I make a single line stave that allows for three different pitches (above the line, on the line, below the line)

Using Staff Properties, you can set the number of lines (and also get rid of the clef):

For Staff / Part Properties see:
https://musescore.org/en/handbook/4/staffpart-properties#staff-properti…