Currently Notion iOS has two voice support in a grand staff. The colors show four voices, but when trying to editi voice three and four voice, Notion iOS assumes you’re trying to edit V1 and V2 in the Staff.
Try it. In a grand staff, say a Bach Chorale, turn SATB into V1 V2 V3 and V4. Make sure voice colors are turned on. Try to edit voice 3 using the V1 or V2 and V3 and V4 can not be edited. I had to turn V3 and V4 back into V1 and V2, edit, then back into V3 and V4
Not smooth during a presentation.