I think to that point, if we want to figure out how you get from solarpunk to fascism, you need to consider what it implies by its analysis (or lack thereof) of the actual material reality that's necessary to make the solarpunk vision come true and how that analysis/blind spots coincide with ecofascism.
What's going on that made dilapidated buildings get overrun by plantlife? Is it massive depopulation? Are we idealizing that?
What's the whole idea about self sufficient communities using technology to live in some kind of frontier? Is this class-conscious, or is it just repackaging settler mythology about frontiersmen and Lebensraum?
And maybe the problem with it "just" being an aesthetic is that it leaves the audience to fill in the blanks for those questions, and I think the default answers aren't great.