Following iOS 15.4.1 release Apple now stopped signing iOS 15.4 preventing downgrade on devices.
Following iOS 15.4 release Apple now stopped signing iOS 15.3.1 preventing downgrade on devices.
According to forum thread there is an issue with macOS 12.3 affecting MacBook Pro 14" and 16" models which had motherboard replacements.
There is a firmware bug in Mac OS 12.3 that renders the update impossible to install on any 2021 14 or 16 inch MacBook Pro that has had it's logic board replaced.Apple Developer Forums
Apple Developer Forums: Monterey Beta Bricking 16-inch M1 Pro MacBook Pro