As a composer for classical guitar, it's common to be writing 2, 3 or 4 voices on a single staff. Access to the voice button in the main palette is tedious. Also, access to the handwriting tool - to switch between handwriting and non-handwriting for dragging notes around - is also tedious.
Ideally, Notion would provide a custom floating palette for user-defined tools so that we can place this floating palette wherever we want, perhaps sticking it to the side of the screen, or simply pushing it around on the display. Tap the tool with one hand and use the Apple Pencil with the other. This would help eliminate some of the tedium and frustration that interferes with the creative process.
Another option might be using LONG PRESS to bring up the custom tool palette so that it disappears and gets out of the way.
But Notion for iOS is coming along great. Very powerful, and very thoughtful. I hope to see this custom tool option ASAP. It would make an enormous productivity difference.