Valve's Steam Deck technically lets you swap the SSD, targets 30fps gameplay - The Verge

Some important details have emerged about Valve’s Steam Deck handheld console-meets-PC — particularly about its target performance level and whether you can actually install your own NVMe SSD to upgrade storage.

In a video interview from IGN, Valve stated that the Steam Deck’s 800p display, capable of up to a 60Hz refresh rate, will be targeting 30Hz for gameplay.

Though, given that most PC games offer a trove of graphical settings to fine-tune, the Steam Deck should be able to achieve smoother gameplay at the cost of graphical quality if you’re willing to knock down a few settings, depending on the game of course.

An article from IGN confirms that you can technically remove and upgrade the storage in a Steam Deck yourself, but the focus is on repairability, not for increasing the tweak factor for the everyday user.