Files got encrypted after upgrading to windows 11

What happens when you click on the file and attempt to open them?
Are you seeing any message?
If yes, would you mind post back the complete message?

If it is less than 10 days since the update, you can try to go back to Windows10.

There are probably no replies, because there is little hope of retrieving an encrypted file. I have tried 😞
BUT
I can say there are some command line options that should tell you what certificate is expected on the encrypted files. If you are lucky, maybe you just need to find your old certificate and import it into your new user account. It has been a long time, but I think a keyword is 'cipher'

https://docs.microsoft.com/en-us/windows/security/information-protection/windows-information-protection/create-and-verify-an-efs-dra-certificate