In your screenshot of a textbook, they refer to it as a convention twice

Left to right is a convention, yes, doing Multiplication and Division before Addition and Subtraction is a rule 🙄

And you still haven’t explained prefix or postfix notation not having order of operations

For the 3rd time it does have order of operations 🙄 You just do them in some random order do you? No wonder you don’t know how Maths works

Get rekd idiot

says person who doesn’t know the difference between conventions and rules, and thinks postfix notation doesn’t have rules 🙄