Hello, Samuel Marshall.
Unfortunately, having an x64 processor is not enough. Windows 11 has very strict security requirements for CPU hardware functions. And Intel processors of the 8th generation and newer meet these requirements.: https://learn.microsoft.com/en-us/windows-hardware/design/minimum/supported/windows-11-25h2-supported-intel-processors
In the very first builds of Windows 11, Microsoft itself, although it did not recommend updating on an incompatible device, did not prohibit it either. And even the official help described a way to bypass the processor check and the availability of TPM, but later this method of circumvention was excluded: https://support.microsoft.com/en-us/windows/windows-11-on-devices-that-don-t-meet-minimum-system-requirements-0b2dc4a2-5933-4ad4-9c09-ef0a331518f1
Unfortunately, there are few official options. Either replace the processor with a supported one (if the motherboard allows it), or perform a full PC upgrade/purchase a new PC, or continue using Windows 10.