Phone APP Design Calcualtions & Buttons

I need help to find some simple software where I can actually design a Phone/Tablet app. I have tried XD and that’s great for prototype but I cant seem to add simple calculations or create buttons to add values to fields. .
I am trying to create a very simple scoreboard with buttons to add or remove points to team A or B. I also want a stopwatch, which can just be a counter, with a start stop and reset function.
I did this in Excel in a few minutes after watching just two videos.
Any help greatly received. I am not looking for free software or even free help I don’t mind paying. This is the first time I have used a forum so I apologize if this does not make any sense.