If you bought your computer after 2010, there’s most likely no reason to throw it out. By just installing an up-to-date Linux operating system you can keep using it for years to come.
The cheapest and most environmentally-friendly computer is the one you already own.
This is my go-to solution - I personally prefer Linux Mint with MATE for a desktop environment.
But if you, like me, have relatives who flatly refuse to use anything but windows (even as they complain about having to relearn the operating system every few years anyways!) then this might be useful to you: https://www.theregister.com/2025/04/22/windows_10_ltsc/?td=rt-3a
Whatever it takes to keep working tech out of the landfill and the potential replacement computers sitting on store shelves.
I really do recommend trying Linux though, it’s been my daily driver for years, including all through college when my windows partition died and I found myself making due with the mint partition I was testing out just to get assignments done. For older computers and Chromebooks Alpine Linux is great but a little more work.