I can't use a keyboard comfortably, and use/develop Numen (https://numenvoice.org) which is FOSS voice control for Linux. Out of the box it's a simple context-free keyboard alternative, and broken wrists is a pretty common use case too.

I'm not sure. I found Artsey the other day though, and it looks super interesting: https://artsey.io/

Maybe you could try something like this(?) If nothing else it's a decent excuse to try something new!

I can’t use my left arm and programming with one hand is very draining. What would you suggest I’d take a look at? Is programming by voice a thing already?

Voice recognition has come a long way, as well as eye tracking. Give it a try, you might be surprised how well it works.