Think the start would be to hook up a display to the Pi and see what happens.
But missing some info tho: How to help us help you - or How to ask a good question
Like what is the install method you used on the Pi? Can u ping the device when you can no longer access HA?
Also why not install 2025.7.1 and then import the backup? if it fails then again after the restore maybe an Addon or integration is to blame.