Lock direction of voice

[HeiPet]

@Andro , you have asked this before and got a perfect answer here:

Change stem direction for a stretch

You can select an existing passage, right-click (or click the Edit menu) > Stem > Force Stem Up or Force Stem Down. You can’t do this pre-emptively; the music has to exist first.

I predict, that you want to hide rests in a voice, that is not playing. Otherwise you wouldn’t have to do this.