With PS Now -a single subscription- you can stream all its (over 800?) games on PC/mobile/consoles, and to download on PS4 or PS5 all its PS4 (including PS2 Classics) games.
GamePass has a different subscription with different list of (150+?) games on PC, console and mobile, with a bigger subsciption (Ultimate, that includes all of them plus XBL Gold plus xCloud). Its games are streamed on mobile, and downloaded on console an PC. Its streaming service xCloud as of now only works for mobile and in some countries, it will be released in the future for consoles, but we still don't know when.
Not all Sony games aren't included in PS Now, and they are introduced there once they have been in the market for a while. MS instead decided some time ago that all the games published by them would be on GamePass at launch.