Microsoft has identified a new issue that may cause problems with those upgrading to Windows 11.
It turns out Windows 11 does not deal well with non-ASCII characters in the registry.
Compatibility issues have been found between apps using some non-ASCII characters in their registry keys or subkeys and Windows 11. Affected apps might be unable to open and might cause other issues or errors in Windows, including the possibility of receiving an error with a blue screen. Affected registry keys with non-ASCII characters might not be able to be repaired.
Non-ASCII characters are commonly used for non-Roman alphabets like Chinese or Tamil.
Due to this issue, if your registry has apps which uses non-ASCII characters in the registry, Microsoft will not be pushing out the upgrade to you. Microsoft also advises against forcing the upgrade using the Media Creation Tool.
Microsoft continues to investigate the issue and will provide a resolution when available.