Having globally routable IPv6 addresses for each device doesn’t prevent you from running firewalls.

Not necessarily true. Celebrities and Nitro subscribers also got early picks, and it isn’t like they wait for each person one-by-one: you are in a bucket with others who might get to your preferred username before you.

Yeah, if you just want to use it personally, you should click Sign In in the menu, then Open Element Web, which brings you to https://app.element.io/.

Alternately Get Started then Download the app.

Either gets you to a client where you can easily create a Matrix account (on matrix.org).

On the tech side of things, the environmental impact of running traditional, centralized services is inherently lower than running any cryptocurrency off of a blockchain. To overcome the technical limitations would be to create another centralized service.

But yeah, there are almost certainly ways that traditional currency can reduce their environmental impact, too.