The Snapmaker 2.0 (at least to code version 1.10) requires an FDISK (MBR) structure on the USB stick with a fat32 active partition in order to show files.
On freebsd this can be achieved with the following commands (where da1 is the raw drive)
First make sure the disk is truly wiped
gpart destroy -F da1
Then create the MBR (this is the equivalent of fdisk)
gpart create -F -s mbr /dev/da1
Then add a fat32 partition to it
gpart add -t fat32 da1
And finally create the actual msdos fat32 file system
This file system once created is recognised by the snapmaker and can be used to do upgrades/print etc…
There will for sure be an equivalent way to do this in MAC/Linux/Windows, the MBR partition table is the important bit that seems to be required.