The FromSoftware tradition of "tutorial bosses that are meant to kill you extremely hard" started with the Vanguard Demon in Demon's Souls. However, it's perfectly possible to beat the boss if you have the skill and patience for it, and that's just as true on PS5 as it was on PS3. IGN shared an early gameplay video of what happens if you do.
Once you kill the Vanguard Demon, it will leave behind a new Archstone that you can use to teleport to the "Unknown Egress". There you'll find some handy items that will give you a headstart in the rest of the game and, uh, against the Dragon God. The problem is that you still need to die somehow to reach the Nexus, which is where Demon's Souls properly begins. And thus, the only way to leave the area is to walk up and introduce the Dragon God's fist to your face.
The new-and-improved cutscene for the PS5 remake makes it clear that if getting walloped by an actual god wasn't enough to kill you, bonking your head on the rough stone floor afterward would definitely finish the job. There's something especially grisly about death by masonry compared to your inevitable demise in the PS3 version.
Thankfully, there will be a bunch of built-in PS5 guide videos to show you the way after that. The Demon's Souls remake will be available as a PS5 launch game as soon as the console starts rolling out on Friday.
If you haven't locked in your order yet, make sure you get the PS5 price you can find.