The term that is often used for that is “source available”. Good example of other software in this category would be what, Unreal Engine?

Heard good things about https://plausible.io/

Heard good things about https://plausible.io/

there is a bridge, but some parts of the fediverse got very mad about it
https://github.com/snarfed/bridgy-fed/
https://fed.brid.gy/

I just have a HedgeDoc presentation and a subdomain on some public FreeDNS domain:
http://testman.kak.si/

Other comments already pointed to some very good software solutions.
But I would argue that absolutely the biggest barrier to entry for the masses is hardware.
Restoring an old PC or making some cable spaghetti with some SBC is currently too advanced for average person.
Self-hosting for the masses would require some new form of home servers.
Something modular, where adding new components would be as easy as playing with Lego bricks.

Does Organic Maps support it?

Something like Cryptpad Form?
https://cryptpad.fr/

GotHub seems to display basic GitHub stuff decently well.
https://gh.whateveritworks.org/

so this is similar to LibRedirect?
https://github.com/libredirect/browser_extension
https://libredirect.github.io/
check out this list of privacy frontends and see if you can implement any of them in Predirect

Also, I see that you only handle one instance for redirect. Either the default instance or custom instance.
Consider implementing multiple instances. Here is list of instances that LibRedirect uses:
https://raw.githubusercontent.com/libredirect/instances/main/data.json
Here is a list of instances that Farside.link uses:
https://raw.githubusercontent.com/benbusby/farside/master/services-full.json

Both LibRedirect and Farside still have to deal with the rate-limiting problem with Youtube and Reddit and I assume other sites as well. Invidious instance or Teddit instance can be rate-limited, resulting in video not playing or post not showing up.
If your extension does not distribute user traffic across multiple instances, then I assume that your chosen instances will get hammered into ratelimit even faster than other instances.
So consider thinking about solution for this.
One of suggestions that I like is to allow user to provide an URL to a list of instances.
That way, someone or some automated system can periodically compose a list of instances and users can “subscribe” to that list.

Also some useful links:
https://github.com/digitalblossom/alternative-frontends
https://github.com/pluja/awesome-privacy#social-networks-and-platforms
https://github.com/mendel5/alternative-front-ends
https://matrix.to/#/#alternative-frontends:tchncs.de

I am aware of those two, but those are just for file storage. I was thinking something more general. Like having a Virtual Private Server, that people can extend with their donated resources. VPS can be used for more than just file storage. It can do processing as well.