This problem exists in both Notion Desktop (Mac) and Notion iOS, I am running Notion 6.8.2 Build 18133, 64-bit on a 2017 iMac with MacOS Monterey 12.3.1, but the problem has been around as long as I can remember (years) on both platforms.
When I am entering notes, for example an octave in the left hand of the piano, I cannot simply select those notes and add an accidental to both of them at the same time. On the desktop, I know that I can select them, hold down Shift, and use the up or down arrows to move them a semitone. That method is not available on the iPad. In either case, it puzzles me that I cannot add a single accidental to two notes of the same pitch class in the same staff of the same instrument simultaneously. I cannot see any good reason for this. If I want to add different accidentals to different pitch classes, I certainly expect to select them individually and change accidentals as necessary. But not octaves in the same staff of the same instrument.
Please think this one through and do something to make this part of note entry more efficient and less frustrating on all supported platforms.
I would love to attach a screenshot illustrating the problem, but do not see an attachment method.