Can I use ea play on the series s independently of the gamepass?
€ A Play is included in the Gamepass, but can also be purchased separately and then runs independently. So you don't necessarily need the gamepass if you are really only interested in these titles.
To your question regarding the app on Series S / X:
Xbox Series S or X
There's no EA Play Hub app for Xbox Series X | S. To download a game or pre-trial, first find the game you want in the Xbox Store for your Xbox Series X | S and then download it from there.
You can also find full games included with your membership by going to My Games & Apps> My Library> EA Play.
https://help.ea.com/de/help/ea-play/ea-play-for-xbox/