Surprisingly, it looks like Microsoft will not put an upgrade block on installations done on a device using Intel’s Pentium 4 661, which was released in 2006 and obviously doesn’t meet all Windows 11 requirements.
As you can see in the above screenshot, Intel Pentium 4 661, which has only one core and 3.6Ghz of clock speed, is listed as a supported processor in the PC Health Check. That’s possibly because Microsoft forgot to update the strings needed to reflect “unsupported status” in the PC Health Check Tool for this particular Intel family.
Disregarding artificial barriers, Windows will run on pretty much any x86 processor – and Windows 11 is no different. You really don’t actually want to, but it does form the base of a cottage community of people trying to get modern Windows releases to run on the oldest possible hardware, which is always a fun exercise.