Steam Deck has M.2 2230 SSD slot, but Valve does not recommend upgrading it - VideoCardz.com
PCI Express to M.2 NGFF SSD Adapter Raiser SATA Bus M2 SSD B Key PCIE Slot Heatsink SATA Cable for 2230 2280 Size m.2 FULL SPEED|Add On Cards| - AliExpress
NEW WD (CH SN530) M. 2 2230 SSD 1TB NVMe PCIe For Microsoft Surface Pro X
Dell 1TB M.2 PCIe NVMe Class 35 2230 SSD PM991 | Dell USA