Hey brother, sorry for the late reply.
I created 2 textboxes. 1 for desktop and 1 for mobile. It takes a lot of adjustments cause you may (as i did) have both textboxes in the same exact place.
First, get the desktop correctly positioned and write down the position. Move that out of the way and forget about it for now. Then create the mobile textbox. Refine the look and size of the box and font size using set css style in event sheet. Like i said, there are a lot of edits here.
Once you have it exactly how you want, reposition the desktop textbox using the position you wrote down earlier.
Then just do it like you would with showing or hiding mobile controls on desktop.
Have the user touch (mobile) or press (desktop) a button... Like ENTER or something else. Then in the event sheet > if mobile > set desktop textbox invisible and disable, and vice versa if on desktop.
If you have problems, let me know.