add custom fretboard diagram to palette

I'm new to Musescore 4 (and a newbie to musescore) and cannot find a way to add a custom fretboard diagram back to the palette. I couldn't manage to find anything in the handbook 4 on this.
In previous versions you needed to hold ctrl+Shift and drag a custom diagram from the score to the palette.
That doesn't seem to work now.
If I click on "more" in the fretboard diagrams palette, the option "add to fretboard diagrams" is greyed out. I am using a custom workspace.