On mobile the context option “Set preview image” on a notebook setcard is missing.
This might have been disabled deliberately and thus already be in your internal tracker. In that case I only want to voice my interest in this feature, because I frequently perform minor edits or corrections on mobile.
Yes preview image editing isn’t supported or tested on mobile, so it doesn’t appear in the menu.
You could disable that feature on mobile and just activate an <input type="file"> when the menu item is clicked. This would pop up an action sheet (on iOS) that allows the user to upload a photo. You can try it on mobile by tapping the 
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