Here ya go: https://panic.com/prompt/

There have been terminal programs for the iPad since at least 2017, when I started using the one above.

As for "custom bespoke software," why would you try to run that on an iPad in the first place? My company has plenty custom in-house programs, but I don't complain that they won't run on a toaster, or a Commodore 64, or a Cray. That's like saying you won't buy a speedboat because it can't carry all the iron ore that your company's dump truck can haul. It just makes no sense.