From what I've researched some months ago on the topic you need to trick Win11 installer (regedit, not tried) or get directly a hacked one (bad idea, obviously not tried) in order to install on a computer with too old CPU.
I would be overly surprised if the official Win11 ISO would work out of the box on an older PC just because it's installed from an USB stick.
I have tested the bootable usb stick on my old device before (old cpu but not older), where windows would say "Your system doesn't meet the minimum requirements for Win 11 upgrade". And it worked despite the message, and now if you meant CPU like a decades old, pentinum duel core or something like those, that I'm not sure of.
Back to the main topic, SSD's are still being dead by this update! I wonder why Microsoft doesn't remove/stop with this version until everything is sorted. I saw some people complaining in a pc related group a day or two ago that, their SSD is dead, and showing as Generic, or isn't accessable anymore.