Yes, this SSD is compatible with the Steam Deck.

Questions & Answers: SAMSUNG 1TB SSD M.2 2230 30mm PM991a NVMe PCIe Gen3 x4 MZ9LQ1T0HBLB Solid State Drive for Surface Pro Steam Deck Dell HP Lenovo Laptop Ultrabook Tablet

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SAMSUNG 1TB SSD M.2 2230 30mm PM991a NVMe PCIe Gen3 x4 MZ9LQ1T0HBLB Solid State Drive for Surface Pro Steam Deck Dell HP Lenovo Laptop Ultrabook Tablet

Brand - Samsung
Part Number - MZ9LQ1TOOHBLU
Model Number - PM991a
Form Factor - M.2 2230
Connection Type - PCIe 3.0x4
Capacity - 1TB
Read Speed - Up to 3100 MB/s
Write Speed - Up to 1400 MB/s
Compatibility - Surface Laptop 3/4, Surface Go/X/7+, Surface Pro 8/9, Steam Deck and more

$199^.50 –