I have tested a rich text field in a form on an iPad using Edge as the browser and see the same behavior. Not sure exactly why it doesn’t work – it does work on safari on the same iPad – and as far as I know Edge uses the safari “engine” on an iPad.
I’ll try to dig some more, but unfortunately there are no way for me to debug this on an iPad as I don’t own a Mac.
In any case I strongly recommend using the TinyMCE option as the default rich text editor doesn’t support for example tables.
Alexander