MuseScore4 (revision757433) on IOS 14.2.1 does not show note insert option. Sometimes the option goes away but can be reinstated by saving file and reopening.
The Note insert option seems to be replaced by a rectangle with dots that does not appear to function as an insert option. When the option goes away, it can be reinstated by saving the file and reopening it.
Comments
What exactly do you mean by "note insert option"? What specifically are you doing - the precise keystrokes you press or buttons you click - and what do you expect see happen, and what happens instead?
If you are referring to note input mode, maybe you've accidentally changed from the default "step time" method to one of the other methods like repitch? If so, long tap the note input icon on the toolbar and re-select the default method.
Oh wait - iOS? The MuseScore notation software doesn't run on iOS. Are you referring to the reader/player app? It has never had any sort of editing capability.