Never heard of it.

I think it’s not a correct expression, and we use “capitalize on” more often which means take advantage of.

You should never ever use "off of" in any sort of formal writing, in any context! "Capitalise on" is correct. But "capitalise" isn't a word you will hear a lot in informal situations, so it's not surprising you haven't heard it. Here are some examples of "capitalise on": https://www.collinsdictionary.com/dictionary/english/capitalise