Note Head palette
In my latest MuseScore version, the Note Heads palette has dropped off my list. I'm not getting any options to customise my Palettes. Searching for Note Heads sometimes brings it up, but there is not option to add to the list. Or sometimes it says 'no results found'. As I'm dealing with contemporary music, this is something I ALWAYS want in my palette list.
Comments
So, when you go into Palettes and click on the "Add palettes" button, what is showing?
"In my latest MuseScore version..."
Please always specify which version you are actually using. You can copy this information from your MuseScore Studio menu path Help > About MuseScore Studio... > Revision > (click the paper icon).
... the Note Heads palette has dropped off my list"
When you use the + (plus) sign to add a palette, MuseScore adds the extra palette at the top of your chosen list of palettes. That has caught me out before.
If the palette really is absent (both from your displayed palettes and from the list available in the "Add palettes" list), then you might try the menu path Help > Revert to factory settings