Here’s how to restore SteamOS boot entry after installing SteamOS update

0. sudo rm /etc/systemd/system/force-steamos-on-next-boot.service

1.Start with Steam Deck off.

2.Hold Volume + button and power.

3.Choose “Boot from file”.

4.Select esp/efi/steamos/steamcl.efi.

5.Wait until SteamOS boots (there will be a blank screen for some time, but Steam should start after that).

6.Go to desktop mode.

7.Run following command:

8.sudo efibootmgr -c -L “SteamOS” -l “\EFI\steamos\steamcl.efi” -d /dev/nvme0n1p1

This will add a boot menu option for SteamOS.

ref: https://www.reddit.com/r/SteamDeck/comments/ywlyyy/help_steam_deck_wont_boot_into_steamos_anymore/

or
In Konsole type curl -sSL https://raw.githubusercontent.com/scawp/Steam-Deck.Force-SteamOS-On-Boot/main/curl_install.sh | bash