Yes, you can use this SSD for the PS5 expansion. It fulfils the requirements with PCIe 4.0 NVMe, M.2 2280 format, over 5500 MB/s read rate and integrated heatsink, which enables easy installation.

Yes, this SSD fits the ASUS PRIME B350M-A motherboard. The motherboard has an M.2 socket (type 2280, M Key) with PCIe 3.0 x4 support, which accepts NVMe SSDs like this one, although the full PCIe 4.0 speed is limited to PCIe 3.0. Note that the M.2 socket shares bandwidth with SATA6G_5/6.

The "P310 Gen4 2280 2TB NVMe PCIe M.2 SSD" from Crucial Technology is not directly suitable for the Steam Deck, as the Steam Deck only supports M.2 2230 SSDs. The Steam Deck has an M.2 slot that is only designed for the 2230 form factor, and mounting an M.2 2280 SSD would cause mounting issues and potentially performance issues.