This is the best summary I could come up with:
After Valve recently launched a stable Steam Client update for desktop and Steam Deck, along with the recent SteamOS 3.4.10 release - SD Cards became a bit problematic.
Sometimes you could pull it out and put it back in and it would appear, other times you might need a reboot.
Quite a nuisance, especially when this would happen every time you turned on your Steam Deck.
Thankfully, Valve just released another Steam Deck update that notes they "Fixed a failure to recognize the microSD card after a system reboot.".
So if you've been having issues make sure you press the STEAM button -> Settings -> System -> Check For Updates.
Nice to see Valve continue to quickly respond to such annoying issues.
The original article contains 135 words, the summary contains 122 words. Saved 10%. I'm a bot and I'm open source!