I have the same issue. The only way I’m able to get the Deck to recognize my usb c flash drive was by powering it off and powering it back on with the flash drive plugged in. Only then will it show up in desktop view and I can mount it/open. However the moment I pull it out I can never get the deck to find it again until I do another power off/on cycle while it’s plugged in.

I wouldn’t call it a solution but I saw a comment on the steam forums that suggested restarting or turning off/on the steam deck with the flash drive plugged in. I can confirm after testing this twice that my flash drive was recognized and I was able to “mount and open”. Of course the moment I take it out and plug it back in then the steam deck goes back to not being able to see it all.

Hopefully this confirms that this really is software related and will get patched soon. For now this band aid helps with what I’m trying to accomplish.

I’ve been on 3.5.7 and still having the issue.