Indeed, that processor is 3 full generations older than the minimum requirement of 8th generation. While it is possible to install Windows 11 on such hardware, Microsoft has said that updates will not be supplied.
This machine should be reverted to Windows 10. In addition, the recommendation for a minimum of 8GB of RAM is a must, even with Windows 10 (and more wouldn't hurt). An SSD always speeds things up, too.
As a matter of personal principle I won't discuss Windows 11 on hardware on which it is not officially supported.