Fenrir supports any size card, as long as it’s formatted as FAT32 with an MBR partition scheme.
There is currently a hard limit of 300 folders in each card, which makes a 256GB card the sweet spot if you want to fit as many games as possible.

We have tested SanDisk and Samsung microSD cards without issues, but all microSD cards should work.
If you do find a particular brand that doesn’t, please let us know!