To summarise: use a terminal server system if you can, using a desktop for the end user that can be made to behave like windows (or another concept that works for your demography), and have the whole setup in a NixOS configuration that you manage in git.

I see that https://github.com/ltsp/ltsp is still going strong.

I'm also a fan of science fiction-like solutions but only in the "oh that would be so cool!" sense, not as a viable solution to the current problem of what could be a runaway greenhouse heating cycle that turns earth into "Venus the 2nd". Keep dreaming, though because what seemed like science fiction just decades ago is becoming reality today and as a future method to regulate earths temperature it seems at least worth a look.

Absolutely. Powered by solar or wind or what other green source is available.

Regardless of the method, carbon capture is not going to work fast enough to make meaningfully change. The only realistic solution to keep earth from going runaway warming and becoming perhaps even another Venus, is to radically increase earth's albedo to a point where the energy balans goes from +2W/m² to -2W/m², using brightening agents like sea salt for instance. In the mean time more realistic methods to manage CO2 en especially also methane levels in the atmosphere can be devised for the longer term.