SD Card should work fine. As one of the tiop guys said it’s a computer.

I put my SD card I used in my chromebook in my LCD Deck just fine. I had it formatted EXT4 which is a standard Linux FS. The Deck itself likes to format in BTRFS. The only issues I had were from RetroDeck and EmuDeck since they couldn’t find the card and I had to manually provide the mount point since it was different than they expected. I consider that a bug in the software, not the Deck’s fault, and the Deck itself worked fine with it.

For the SSD I assume you intend to get a small sized OLED Deck and replace the SSD with your existing SSD. In that case I’d recommend checking teardowns to see if the SSDs changed at all between the models first to be sure it will be compatible. Also if your SSD manufacturor (assuming you have a third party one you installed) specifically supports Deck you may want to ask their support if it is compatible with the OLED Deck. They probably know already (whether their support person knows… who can say).

No guarantee the software on the SSD will be the same; right now the recovery image for Steam Deck is just a single download. If they add a separate one for OLED by release, that’s a sign you’ll need to reimage the SSD or the software might not work properly. You might be able to keep your user data though and just reimage the OS.