Hi there,
Yes, only 8th generation processors are supported for Windows 11. This is been specified by the PC manufacturers for improved security and performance. It seems i5-7400 is not on the list of supported processors.
Windows 11 supported Intel processors
https://learn.microsoft.com/en-us/windows-hardware/design/minimum/supported/windows-11-supported-intel-processors
----------------------------------------------------------------------------------------------------------------
If the reply is helpful, please Upvote and Accept it as an answer