I finally got a PS5 from Amazon, it arrives on Sunday. This is my first Playstation console ever. I never had a PS3 or PS4, but I’ve had Switch, PC and Xbox. What are my must plays? I have Gamepass on Xbox so I probably won’t get the PS+ equivalent one, I’m mostly looking to play first party stuff like Spider Man and Horizon.
Play Astro's Playroom to get a feel for the Dualsense controller's features. It is probably not going to resonate as much for you though if you have no nostalgia for previous Playstation devices as a lot of the collecibles are old Playstation devices (PS1,PS2,PS3,PS4,VITA,PSP,etc). It is a good platformer/puzzler in the vein of a Nintendo Mario game though.
After that, just look through the Playstation Collection and figure out what genre of exclusives interests you. I personally enjoyed Horizon Zero Dawn, Uncharted series, God of War series, Last of Us games, Spiderman, Detroit Become Human and Until Dawn. Some of those are also now on PC though. There are other exclusives I intend to play but haven't yet like Bloodborne, Days Gone, Death Stranding, and Ghost of Tsushima.