If your Steam Deck gets stuck during the boot logo (or during the "verify installation" phase after an update), there are different options you can try to get it booting again like putting the device in battery storage mode or with one of the methods described in the Official SteamOS Recovery and Troubleshooting.
For me, neither the battery storage mode nor booting the old version helped and resetting the device was the option I tried to avoid. In my case, I found another way to restore the device without loosing my data on the device but you will need a physical keyboard attached to the Steam Deck:
- Hold the power key for a few seconds until the screen goes blank
- Press the "three dots" button and the power key to get into the boot menu similar to the "Rollback to previous OS" option of the official guide
- Choose the entry with "Current SteamOS-[...] + Boot Menu"
- You will see another boot menu (from the Grub bootloader). Now attach the physical keyboard, e.g., using a USB-C docking station with an attached regular keyboard
- Press the "e" key to modify the boot menu entry
- Move the cursor to the line starting with "steamenv_boot". As this is a long line, the line wrapping makes it appear as multiple lines but you have to press the right arrow key or the "end" key to get to the end of the line.
- At the end of this line, add " systemd.debug_shell" and press F10
- The system will boot now until you only see a blinking cursor. Now press CTRL+ALT+F9 and you will see a shell prompt.
- Enter "df -h" and check the size in the "avail" column in the line where "/home" is in the last column.
- In my case, the home partition was almost full and after freeing some space, the Steam Deck was booting again. I deleted the mesa shader cache, which had a size over 1 GB, with the command: "rm -r /home/deck/.local/share/Steam/steamapps/shadercache
- Check the space again with "df -h" and then enter "reboot" and the Steam Deck will restart after a few seconds. In my case the first boot still took a little bit longer than usual but eventually the boot into the graphical user interface completed successfully.