The method isn't too different from the PS3 and 4 but Microsoft really beat them in the storage expansion department. A similar NVE drive for the PS5 is about ~$20 more than the Mircosoft option and faster but the simplicity of the the Series X|S is nice. The PS5's option is a lot more flexible and futureproof though. Ive take drives from computers and put them in playstations and back with the other consoles, you'll be able to do the same with the PS5.
I'm waiting to see how well the PS5's OS will handle two drives (two internal drives). Sony has been trying to downplay people's expectations, at least from what I've seen.