When georeferencing a page, you can select a GCP and hit the trash can button to delete it. The same option would be useful for multimasking on mobile.
If this request is linked to a problem, please describe.
This is especially an issue when trying to save a multimask and getting an error about a specific overlapping/self-referencing control point. Even if you can figure out which point is the culprit (which itself is a chore — maybe the faulty point could be highlighted a new color?) I can’t find a way to remove the control point on mobile. This leads me to having to delete the layer mask and start over.