Sweet jesus I had a fun day.. Upgrading my 64GB to 256 was a nightmare, I thought I'd genuinely broken it at one point...
Opened up the Deck and swapped the SSD (easy enough)
I put the OS image onto a USB flash drive and used a USB C adapter, booted into recovery mode and... It sat there doing nothing.
Rebooted, nothing. Re-did the iso in Windows, nothing.
So then I read to use the sdcard slot instead as it's faster, I only have the 1 card, so I lost all my installed games and put the boot image onto it.
Booted off the card fine, chose the full restore option and, it seemed to start up OK then the terminal just closed... Aaargh!
I then had to go spend time with my family on a day out, how annoying
When I got home I tried to boot from the SD card again but it wouldn't boot to desktop, it kept throwing up errors. I reformatted and re-imaged the card twice, redownloaded the image even but no joy!
So I went back to the USB drive, it slowly... Veeeery slowly booted to the desktop (2nd try) and eventually it did its thing.
I then rebooted and.... None of the buttons worked, no track pads, buttons, nothing... The touchscreen did though and I connected to WiFi and... It updated, then got stuck on the "starting steam deck update download"!
Another reboot and it updated, rebooted and.... It works fine!
That's 3hrs of my life and a lot of stress but I now have a 256GB deck upgrade for £18!