For your 2nd build that doesn't qualify for W11, there i suggest that you install any GNU/Linux distro onto it. To have up-to-the-date OS on it.
Linux Mint is most similar to Win but you can choose any distro you like.
Guide on how to create installation media + installing GNU/Linux distro:
https://pendrivelinux.com/universal-usb-installer-easy-as-1-2-3/
E.g;
One of my elderly relatives has laptop that has Win10 on it, but not qualified to run Win11. Rather than junking otherwise fine working laptop, i'll be installing Linux Mint onto that at some point. After all, they only use it to surf the web and for that, it doesn't matter what the OS is, since browser is still the same.