Now that the M.2 slot is open, it's time to insert the SSD. Begin by carefully putting the SSD into the slot at a little angle, making sure that the notches on the SSD match with the key on the slot.

Corsair MP600 Mini M.2 SSD The Corsair MP600 Core Mini is a 1 TB SSD that’s compatible with the Steam Deck and ROG Ally, providing either handheld more space for games without having to rely on ...

Modders can install full fat 2280 size M.2 SSD inside the ROG Ally by modifying some parts of the Ally's clamshell.