Is it really that no one at all will pay or not enough people will pay to turn it into a billion dollar VC funded business? Could such a business perhaps be bootstrapped (while keeping a stable full-time job) and built with more modest goals in mind (say just support yourself and a small team)?

To be on the scale of social media, you'll need to be a profitable billion dollar business.

Nobody has supported billions of users with modest goals. It's nearly an oxymoron.

I am grossly aware of features not always being the answer - but - i think that there are features built into the app im building that will create value. Whether it is enough value, only customers can decide!

If you want to make money with digital services, you have to make them for businesses, not end users. End users are used to not pay, and they never will, which means you either monetize with ads or by selling user data. There is no third option.

Donations and optional payments are very niche and not something that can build a sustainable business.

Understood, but people also pay for ad-less subscriptions too. Pay for Social Media without Ads? Just a hypothesis