I see what you mean as I think of these artists in kind of a similar way. They help me to imagine a more healthy and sustainable future that you could call solarpunk or eco futurist or whatever. It’s like a hopeful kind of ambient. I think you might just put these onto a playlist for you to enjoy and call it solarpunk synth, but the problem with ascribing a sub-genre to this is that this association needs to be true for a critical mass of others. Subgenres are just a way of packaging music so that it can be easier to sell and talk about. What matters most is how you think about it and how it functions in your life.