Perhaps more details are involved behind that notice.
And more than one fault, could cause similar message.
One of those may find remedy (or not) from here:
• If you can't activate your iPhone - Apple Support
//support.apple.com/en-us/HT201407
• If you can't update or restore your iPhone or iPod touch - Apple Support
//support.apple.com/en-us/HT201263
• If you see the Restore screen on your iPhone, iPad, or iPod touch - Apple Support
//support.apple.com/en-us/HT203122
(If there was a message on the iPhone screen, it matters what it said.)
• How to Fix Unable to Activate iPhone (2022) - TechCult
https://techcult.com/fix-unable-to-activate-iphone/
Some ideas within an article such as this, have individual uses
and a few of those could help restore your iPhone functions.
Passcodes are another matter to deal with ~ anything is likely.
• iOS15.4/15 - How to Fix 'Find My' - Unable to Connect to Server | itoolab
https://itoolab.com/fix/find-my-unavailabe-unable-to-connect-to-server/
[..Don't download -any software this site may suggest- try basic steps only.]
Not sure what else to suggest; a backup to a computer could be restored
by lightning cable to the iPhone; or there may be backup in iCloud still.
