Rhythmic editing of tied notes

This is not to say that you have to start with a rest in order to create a tuplet. You can start with one note, you just can’t (yet) gather multiple notes into a tuplet. Right?

You can’t gather an existing single note into a tuplet, either. If you have a note selected and start a tuplet at that position, the existing note will either be overwritten or the tuplet will be inserted before it, depending on whether Insert mode is active.