How to combine notes into a single note. If the 2nd voice is a note with a dot?

That's correct.

Step-wise however:

   • Select the shorter duration note head
   • Press v to make it invisible

Result: The notehead turns gray onscreen IF you have View>Show>Invisible checked. Regardless invisible notes will be invisible in print or PDF. With View>Show>Invisible unchecked the notehead will be fully invisible onscreen.

Here's a walk through workflow example:

This is my source score—where I generated the image attached in the previous post. There's a good chance I'll continue to update the score, but perhaps not the posted image.

NOTE: MuseScore.com renders scores as hardcopy:

• So even though the score has View>Show>Show Invisible checked you don't see the gray quarter notes "behind" the half notes in measure 4 on .com (because they don't show in hardcopy.)

• However, if you download the score and open it in MuseScore 4.4.1 you will see the gray quarter notes ... and you can suppress their visibility by unchecking View>Show>Show Invisible.

https://musescore.com/user/35880724/scores/20503927