I just ordered a Ryzen 9 3900x and I got a Asrock 5500xt are they compatible?
No SAM with your card model.
As for 3900X, i assume you have checked compatibility with your motherboard and whether the board maker will/can supply a bios update if you decide to upgrade to a new Gen. card later..
I have a Asus 570 tuf mb and in the bios it shows it there but my current cpu is a Ryzen 7 2700x and I not it's not working with that.
I've just looked at the rx6700xt reveal vid., where they also announced SAM coming to Ryzen 3000 (not the G models), you still need a RX6000 series card and a 5xx series mobo though.