Hello Stuart! My name is Abdullah, and I will assist you today.
I am sorry to know that you are experiencing this issue. Do you get the message when you are trying to install Windows 11 from a USB thumb drive? If yes, then it is because your processor doesn't support Windows 11. Please check the supported processor models listed below:
https://learn.microsoft.com/en-us/windows-hardw...
If you cannot find your processor model on the list, then that means that the processor model you have doesn't support Windows 11.
In case you are still interested in installing Windows 11 on a computer that doesn’t support it, you will need to have a Windows 10 operating system running on your computer. Please check the Warning part of below article and follow the instructions to upgrade:
https://support.microsoft.com/en-us/windows/way...
Thank you.
Best,
Abdullah