In case you are running Windows 10, try run PC Health Check app and it will tell you if your device is compatible with Windows 10 or not.
Have a look at:
You may see list of compatible processors for Windows 11 on:
And your processor is not listed and it means , it is not compatible. You my file a report in the Feedback Hub app or upvote existing ones and request your processor become compatible. To learn more why Microsoft make such a decision, have a look at: