PS5 Doesn't Feature Xbox Series X/S-Style Quick Resume Game Swapping
At least at launch, you'll need to boot up your games from scratch when jumping from one to another.
One of the big features that Microsoft has touted with Xbox Series X and Series S is Quick Resume, allowing you to bounce back and forth between multiple games without having to exit one and boot up the next one from scratch. If you were hoping the NVMe SSD that the PlayStation 5 is equipped with would allow for something similar, you're out of luck: Quick Resume doesn't exist on PS5, at least at launch.
When you're playing a game on PS5 and switch to another one, you'll have to exit out of your current game and start a cold boot on the next one. Fortunately, the speed of the PS5's SSD does mean that starting up a game that isn't running is much faster than what we're generally accustomed to on current-generation consoles. However, the ability to essentially be playing multiple games at once doesn't exist. That means you'll need to find a save point in, say, Demon's Souls if you don't want to lose any progress when you decide to join your friends for a match of Call of Duty: Black Ops Cold War.
It's possible that Sony could implement a Quick Resume-style feature at a later time, but for now you'll need to deal with a slightly more traditional setup when it comes to juggling multiple games.
Another point of differentiation between PS5 and Xbox Series X/S is that the latter allow next-gen games to be stored on an external drive. You'll need to then move them to the system's internal SSD or expansion card in order to play next-gen games (backwards-compatible games can run off an external drive). On PS5, next-gen games can only be downloaded to the internal SSD (although, again, you can play PS4 games off an external drive).
For much more on what to expect from the new console, check out our PS5 review.