itch.io

Here is one software renderer that is very efficient and is completely free to use, it's even in the public domain. https://codeberg.org/drummyfish/small3dlib

I don't expect you to use it for this game, however. Maybe it's possible but perhaps it's best if a new, smaller game is made using it one day. If you'd be interested, of course. 

I know a lot of devices have some kind of GPU built in, but they still rely on drivers and a bevvy of third party libraries to get working. It's not as universal as something that is CPU-reliant, because we've had CPUs a lot longer than we've had GPUs. A game like Doom, which was initially designed exclusively for software rendering, stands the test of time because it isn't restricted by APIs and the like. Because it was eventually licensed under the GPL, and because it was coded so well with portability in mind, people did eventually add GPU-centric features. But you aren't going to play Doom via GZDoom on every device, while the stock CPU rendered version can be played on almost anything. Even a pregnancy test lol.

It's not often a case of you 'should', but because you 'can'. I think games should be a thing that you can modify however you want, and port it to newer platforms as time passes.