Creating custom templates
I used to know how to create custom templates and I used to have some that I frequently used; but I haven't been using MuseScore much for a while and my templates seem to have disappeared — maybe from one of the updates or when I transferred files to my new computer.
Anyway, I have forgotten how to do it and I can't seem to find directions in the online handbook. Can someone point me to the right page?
Simple: just save the score in your personal templates directory
Templates are regular scores saved to a configured folder. See https://musescore.org/en/handbook/3/create-new-score#templates for where to find that folder.