Chrome OS 91’s most recent update, version 91.0.4472.147, began slowing performance on Chromebook laptops, leading to Google pulling the update for the time being. Unfortunately, rolling back to a previous version (91.0.4472.114) has created a new problem. As reported by Chrome Unboxed, this change has broken the Linux container and will prevent attempts at installing Linux.
It seems the issue is tied to the version update process, itself. Since the 91.0.4472.147 update no longer appears as the latest version, users who are running or have reverted to 91.0.4472.114 will be told they have the latest version installed. This won't cause problems by itself, however if you try to install Linux you'll be told you need to update Chrome OS—and then you'll be told you're already running the latest version.