I’m just spit-balling here but…
I have found some computing devices will only recognize an external drive using the Master Boot Record (MBR) partition type vs the GUID partition type. That’s because GUID puts two partitions on the drive. Partition #1 is the “MBR replacement” volume, and Partition #2 is the user volume (the one you’re supposed to see).
I’ve encountered situations where only partition #1 is detected (which is not the user volume) and then the drive either won’t mount, or it appears empty.