There has been an interesting trick, a single command, that allows unsupported CPUs to bypass Windows 11's system requirements check during setup. That has seemingly stopped working on very old chips.

Microsoft said my PC was 'too old' to run Windows 11 - how I upgraded in 5 minutes anyway ...

The first Windows 11 24H2 Insider build was eventful as it brought many new features and improvements while also confirming a shift in CPU ISA support. The next one builds on top of it. Microsoft ...

Don't Throw Away Your Laptop: How to Install Windows 11 On Unsupported Hardware ...