Sadly the issue with this is that you can offset both the cost and the carbon impact in just few years. (I say sadly because of course I'd much rather people would reuse than put working hardware to trash)
If you want to save power get a used Atom (like the one in my T100TA). The are also very cheap. A Dell Wyse 3040 (2GB RAM fixed) for example consumes 4W idling and < 10W under max load. CPU Power is a bit better then the Raspberry Pi 4. And it's only 40€/$
Buying appropriately sized, used hardware will have a better footprint.