The mass storage in valves handheld console steam deck can not only be expanded by using a micro sd card. The company relies on an m.2 slot with pci express connection. In the two more expensive versions, this is occupied by a 512 or 256 gb of gross pcie ssd, which can be exchanged. The hook: it matches 30 mm short ssds (m.2230), which are hardly reliable in retail and relatively expensive.
In the most favorable variant for 420 euros this m is.2 slot also available, ex works but blank. Valve released 64 gb emmc memory. Who buys this version, can optionally be able to reduce a faster pcie ssd.