My belief that 6th-8th gen cores were practically identical turned out to be wrong.
Kaby Lake introduce something called Mode Based Execution Control. Microsoft uses it for something they call
Hypervisor-protected code integrity
HVCI protects modification of the Control Flow Guard (CFG) bitmap.
HVCI also ensures that your other trusted processes, like Credential Guard, have got a valid certificate.
Microsoft defines
Control Flow Guard as
Control Flow Guard (CFG) is a highly-optimized platform security feature that was created to combat memory corruption vulnerabilities. By placing tight restrictions on where an application can execute code from, it makes it much harder for exploits to execute arbitrary code through vulnerabilities such as buffer overflows. CFG extends previous exploit mitigation technologies such as /GS, DEP, and ASLR.
HVCI is an optional feature of Windows 10, and it appears to become mandatory in Windows 11.
In summary: 8th gen (and many? 7th gen) have new security features that Microsoft considers so important they are willing to strand a significant proportion of their userbase.