I said "M pa t we pyès moun la" and was told that "pyès" is out-of-date, that only old people will understand it, and that "okenn" is way better. Is this true?

"pyès" is not outdated. How could it be?

What you will find is that people from a specific region of Haiti tend to use "pyès" more than others.

You are correct to say: M pa't wè pyès moun la.

Other synonyms for pyès moun are: okenn moun, pèsòn

So, you could also say:

M pa wè okenn moun la.

M pa wè pèsòn la.

Also Creole speakers will use pyès to mean none as in:

There will be none of that.

P'ap gen sa pyès.

I have no money on me.
M pa gen pyès lajan sou mwen.

She doesn't have any children in Haiti.
Li pa gen pyès timoun Ayiti.

Ask me anything