"If you’ve been paying close attention to PS5 news, this won’t be a big surprise. PlayStation hardware architect Mark Cerny
spent several minutes talking up the SSD storage expansion feature as part of his technical preview back in March, but he also said at the time that support was likely to be “a bit past” launch. What’s the holdup? As Cerny explained, not all M.2 SSDs are fast enough to keep up with the PS5, thin enough to fit into the SSD bay, or compatible with Sony’s I/O controller — and Sony promised to do compatibility testing late this year to make sure.
At the very least, Cerny suggested, off-the-shelf SSDs would need to deliver more than 5.5GB/sec of bandwidth over a PCIe Gen4 connection, and not have a giant heatsink so large that they won’t fit into the PS5’s drive bay."
Sony confirms the PS5 won’t support SSD storage expansion at launch