I use a mid 2009 Core 2 Duo. I replaced the battery on it ~6 months ago. I also installed Mojave on it, and with the exception of a weird quirk where apps that do not live in the Dock do not disappear from it when you close the app, it runs fine.

It is essentially a Hackintosh, albeit a legal one, as the hardware is Apple hardware.

I do dev work on it, though it is ruby and/or javascript, not a lot of true compiling happening. But it works well.

I'd love it to be officially supported, but I mean you have to draw the line somewhere.

Edit: I forgot to mention the SSD I put in it, or the RAM I maxed out. (I did the upgrade work, I was not about to pay the premium for Apple to do it.)