Right, I'm [redacted] years old and can't believe I haven't got a go-to solution for this yet, but there it is. I need to cannibalise other people's knowledge instead.
This is my hair. It is wavy, abundant, and always dry and frizzy from about halfway down. I wash it every other day because I've learned the hard way that any more or less is wrong, wrong, wrong! Anything I have ever tried to use on it to counter the frizz either doesn't work if I put it on wet hair, or immediately over-shoots and turns it into an oil slick if I put it on dry.
I usually lose patience and cut it off, only for the cycle to start again, but for boring reasons I have to keep it long at the moment.
What one product- and I really do mean one - do I need? Ideally to be used on dry hair unless you SWEAR it will do something if I do it on wet. 😂