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Amazon.com: SABRENT Rocket Q4 2230 NVMe 4.0 2TB High Performance PCIe 4.0 M.2 2230 SSD Compatible with Steam Deck, ASUS ROG Ally, Mini PCs [SB-213Q-2TB] : Electronics
Steam Deck has M.2 2230 SSD slot, but Valve does not recommend upgrading it - VideoCardz.com