The Steam Deck will format the microSD of your choice into the Linux-based format, EXT4, so long as you use any compatible SD, SDXC, or SDHC microSD card, you're good to go.

How to Format a Write Protected Kingston Micro. Kingston microSD and microSDHC are miniature versions of standard SD cards. This tiny memory cards are designed for portable devices, such as phones ...

A 2TB SDXC card would be able to contain as many as 100 high-definition movies, or around 4,000 photos in the professional RAW format.