I really don't believe in trashing computers. That Air can probably still run emacs and ssh in 2030. That alone can be valuable.

The biggest problem is usually the battery just plain giving up. Sometimes blowing up like a balloon and damaging the case. Unfortunately Apple makes it quite challenging to replace the battery on an Air, or any of their modern laptops.

On the older airs, it's very simple. I finally got around to replacing the battery on a 2011 air that I still use every day. Cost about $65 and took about ten minutes. The kit even came with the odd little screwdriver bits I needed.

I’ve got a 2013 Air. I’ve replaced the battery twice and doubled the size of the SSD. Compared to replacing the battery on an iPhone, it’s a piece of cake.

Just buy the battery from iFixit and follow their online instructions.

FWIW my 4gb 2012 air runs latest OSX pretty well. I mostly just run terminal and Webstorm. Gotta watch those chrome tabs lol

FWIW my GF has just finished her Master’s thesis on my old 4GB 2013 Pro. So apparently it’s still good for that.

I don't know how much of a limitation 4GB RAM is; but with NixOS, I'd also worry about storage space.

I run NixOS on several old Chromebooks with 2 GB RAM and 16 GB drives. It's doable if you stay on top of garbage collection. YMMV depending on your use case.