Updated 01192023-034109
There are now quite a few terminal emulator-esque apps on the App Store, but I've been using a-Shell since it was joined only by Blink (from which it was forked) and iSH. As it was then, a-Shell remains the only one of these with which one can actually accomplish command line tasks locally beyond screwing around. I am ultimately not a command line native, and I don't have the basic theory beneath my use of Python scripts, yet I've been able to accomplish startlingly powerful things within this app, thanks in large part to gracious and immediately-available support via the project's Discord server.
If you've found yourself here by way of a Siri Shortcut's requirement, I would encourage you to take the time to investigate the commands said shortcut(s) run - try running them yourself!