And I am not sure which I should start with.  All of these will be first time experiences as I stopped buying PS4 games after TLoU2 in order to be able to play upgraded versions on the PS5 I would have gotten eventually.  What I have so far is...

Ratchet and Clank A Rift Apart

Demon Souls (did play this on PS3)

Miles Morales Ultimate (with the first game I have not yet played included)

Deathloop

Returnal

Ghost of Tsushima Directors Cut

As you can see I have quite a bit to choose from.  Any suggestions out of these games?

I don't own a PS5 or any of those games.

But I feel like Ratchet and Clank is a solid start. After that, you can choose based on your preference of genre.

Open world chillness- Ghost of Tsushima
Hardcore action- Demon's Souls
Satisfying gameplay- Deathloop or Returnal
Marvel Story/ Superhero- Spiderman

First of all I’d recommend playing Astro’s Playroom first. Its a fantastic intro to the system but as someone who also just got one Ive been playing thru Spidey Remastered for the first time and it also a very good start

I would make it so that Spider Man and Ghost of Tsushima are apart from each other. I get open world fatigue.
But what to start with? Would perhaps also depend on what you played last.
If you don't mind playing 2 at the same time, I would suggest Ghost of Tsushima (which is the most last gen of the bunch) with quick rounds of Returnal in between to freshen things up (games with "runs" or "rounds" are ideal for quick little sessions).
Perhaps you can exchange GoT with Spider Man, whatever you feel more like starting in the moment.

I'd say spiderman first, its an amazing game, but leave a break before you play miles morales, as it can get to be too much.

Demon souls is good but more likely to frustrate you, not a first experience you should have with a new console.

Personally I'd just play returnal, my favourite ps5 game so far, but its not for everyone so I'd say spiderman just to be safe.

I don't get what everyone else sees in astro. I played it for maybe 10 minutes and didn't like it, it was bland, not engaging. I'd recommend just skit that game and play the better games. I started the ps5 with assassins creed and it was amazing, why waste time with astro.

I got the plat for Bloodborne, I think I will be ok with Demon Souls lol.  My patience for these games has been tempered long ago, since I got the original Demon Souls on the PS3.

Anyway I am leaning toward Spiderman, then Ratchet, then Demon but we will see how it plays out.  I know GoT is the most "last gen" of the bunch, but I was REALLY hyped for this game when it was announced.  Just never got around to playing it and when the PS5 released I decided to wait till I got one in case a gen 9 upgrade was released (which it was).  So I dunno, maybe I will do that one first.  I just feel like the Spiderman Remaster might be enhanced more for PS5, and want to be wowed so to speak.

While your recommendation is fine and may or may not fit Shiken's taste, I would lean towards at least starting off by dipping my toes into Astro for a few reasons 1. positive recommendations vastly outweigh the negative 2.it is short and so makes a good appetiser while showing off the controller.

I don't own a PS5 and I won't for a couple of years, but Kena: Bridge of Spirits looks really nice. If I don't play it in Epic, I might pick it up when the time comes in my PS5 Slim.

Jealous that's a good lineup of games to try, not played any of those (unless you count Spider-Man PS4 for the remaster you got with miles).

Ratchet seems like a good introduction to the console and it's features to start with. Plus it's one of my favourite series.