Split The Bill
This Shortcut performs just as well, if not better, than most of the iOS apps in the App Store built to do the same thing.
It allows you to enter the bill amount and, if it’s not included and you feel so inclined, to add a percentage tip from the list provided (5%, 10%, 15% or 20%) or a custom percentage of you own choosing. If you prefer you could just add a fixed amount rather than a percentage.
The shortcut then splits the bill equally between all those paying.