Sony has announced that the next PS5 beta firmware will let users expand their storage via an NVMe SSD. The SSDs need to be PCIe Gen 4 compatible and offer a sequential read speed of at least 5,500MB/s. Drive capacities can range between 250GB and 4TB.
https://www.notebookcheck.net/PS5-SSD-storage-expansion-is-finally-here-but-only-on-the-beta-firmware-version.552668.0.html