Is there any way to downgrade it without SteamOS automatically upgrading it again on next boot?
The way I see it right now there doesn’t seem to be a way to do so unless you’re a Windows user (as that one doesn’t automatically upgrade it on boot).
I don’t think so but why would you want a downgrade?
I just made a tool for that - Steam Deck BIOS Manager.
Steam Deck BIOS Manager -
https://github.com/ryanrudolfoba/SteamDeck-BIOS-ManagerEasily backup, unlock, flash, block / unblock BIOS updates. No BIOS / binaries provided - it downloads it straight from evlaV gitlab. md5 sum used as a sanity check to make sure the downloaded files are not corrupted / tampered.
Github -
https://github.com/ryanrudolfoba/SteamDeck-BIOS-ManagerVideo demo -
https://youtu.be/hp5ue4m2Xus