By band “diamond” I’m referring to the notation the symbolizes holding the chord (usually the value of a whole or half note), it’s pretty commonly seen in contemporary band chart for pop music.
Right now the only “diamond” notehead I see on the palate is the small diamond that means playing a harmonic.
The only closer option I have is the insert a semibreve (whole note) and then toggling that into slash notation, but that is still not the diamond I was looking for.
(I’m currently using the latest version of musescore 3.)