Reticulum is a decent candidate for this (in that it's purpose-built for more than texting).

There's a couple good beginner's introductions here:

https://www.carstenboll.dk/reticulum-a-beginners-guide/

https://github.com/samuk/awesome-reticulum/

Reticulum is a whole cryptography-based network stack which feels like it was developed from the ground up out of radio networking protocols. It can run over the same LoRa radio devices Meshtastic and Meshcore can use, but it can also use ad-hoc WiFi, data radios, modems, serial lines, amateur radio digital modes, and it can even tunnel through the Internet (meaning you could set up a local mesh of LoRa radios, old personal computers and laptops, and whatever wireless routers and other networking gear you can find, connect a neighborhood together using Reticulum as the underlying network, then connect that through the internet to Reticulum networks anywhere in the world. You can write software to run on Reticulum, and it already has a bunch of programs like NomadNet which can do encrypted messaging (same goal as Meshtastic and Meshcore) but also host and view text-based web pages and I think some other stuff. In a lot of ways, this one feels like the meshnet you'd see in a scifi book, an all-encrypted network stack that allows you to just link together any old hardware you can scrape together and rebuild a decentralized version of the internet grounded in much more secure protocols. (I'll admit I straight up don't understand how a lot of this works on the network/cryptography level, it actually seems similar to Tor in some ways but I don't understand that very well either.)

On a small scale, yes. But just like how you can claim some land, the strong country who also claims that land can use violence to protect their interests. So if you start building towers or laying cable across the streets, they'll smack you down and throw you in a box. Their feeble minds are so twisted by "law" that they can somehow justify this morally.

The other option is a network of nodes, until those nodes are deemed a risk. Plus the extreme amount of overhead that comes with them.

https://meshtastic.org/

Yes, it is. The hardest part is physically connection across long distances. You can peer with other ISPs though so you can still get partial, regional autonomy.

It's not necessarily easy nor cheap but it is within their own possibility. You would start with a wireless ISP, you get ISP grade unlicensed bandwidth equipment to connect your customers back to a home office with an ixp link, and then you grow from there. Supporting publicly owned fiber optics trenches with plenty of space would make it easier for smaller companies to install wired infrastructure that serves homes and businesses but that's a generational infrastructure project.