Interesting stuff, thanks for posting. The Lilium plane looks fascinating, I hope it flies!

To me a practical short term solution is solar powered green hydrogen, which if we got into it in a big enough way, would solve a lot of the problems we are seeing with environmentally sustainable long distance flight.

Here is my take on how things could start off:

https://eric-bott.medium.com/self-contained-solar-powered-community-system-517021711db9