https://wccftech.com/ps5-no-ssd-storage-expansion-at-launch/

With the launch of the PlayStation 5 and Xbox Series X, players are really going to have to start thinking about storage again. Both consoles feature speedy solid-state drives, which will greatly reduce load times, but the days of expanding your storage by plugging in any old portable hard drive are over. In fact, it seems you won’t be able to expand your PS5’s storage at all at launch. That's a bit of a potential issue, as the PS5’s built-in SSD offers 825 GB of storage, with only about 670 GB of that being useable for games.

Microsoft and Sony are taking different approaches to storage expansion for their next-gen consoles. The Xbox Series X and S will offer easy plug-and-play SSD expansion cards, with options from various manufacturers eventually being offered (a $220 Seagate 1 TB SSD expansion card will be your only choice at launch). Meanwhile, the PS5 will be compatible with regular off-the-shelf M.2 SSDs, but you’ll have to open up your console’s casing to install them.