According to this troubleshooting guide, one is to install gnome-keyring to allow the launcher to store the account info. This, however, is impossible on the Steam Deck as the file system is locked.
Please update the launcher to not need this (other apps seem to have a different way of doing this) or update the guide to include SteamOS users.
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We're tracking this issue in MCL-21181, so this ticket is being resolved and linked as a duplicate.
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