Start with Astro's Playroom and if you like it get Astro Bot! It's an excellent game and won GOTY for a reason! Play Ratchet and Clank - Rift Apart too! It's on PC, but it's a game that's meant to be played on PS5! Demon's Souls is another exclusive as @AnKsaid!
The thing is - this gen Sony has moved away from exclusives and only Nintendo is there for exclusives! True - Sony's games release late on PC, but they do! So you have to play on prices! What's full price on PC is PS+ free or bargain bin on PS5 (either digitally, on PS+ or physically), and these include major games like Last of Us Part 2, Horizon: Forbidden West, God of War: Ragnarok, Spiderman 2 etc (Not to mention - Sony 1st party games are generally best played on PS)