For individual projects the way this usually works is one of the larger companies that rely on the project hires the developer as an employee to maintain the codebase full-time and help integrate it with their internal processes.

Larger projects might form their own company and sell integration & support to other companies (e.g. Red Hat, Bitwarden).

Otherwise you're basically dependent on donations or government grants.

There's a Wikipedia article on this subject: Business models for open-source software

And there's various industry opinions:

Demystifying the Open Source Business Model: A Comprehensive Explanation

How to build a successful business model around open source software

Open Source Business Models (UNICEF course)

I think monetization is easier for user-facing software though, which a lot of this material is written around, and harder for projects like libraries.

Daniel Stenberg (author of curl) has written a little bit about his journey working on curl: https://daniel.haxx.se/blog/2020/10/26/working-open-source/

I now work for wolfSSL. We sell curl support and related services to companies. Companies pay wolfSSL, wolfSSL pays me a salary and I get food on the table. This works as long as we can convince enough companies that this is a good idea.

The vast majority of curl users out there of course don’t pay anything and will never pay anything. We just need a small number of companies to do it – and it seems to be working. We help customers use curl better, we make curl better for them and we make them ship better products this way. It’s a win win. And I can work on open source all day long thanks to this.

The problem is the people who use the library don’t have access to the money. They’re just some dev trying to build something and your library is one of their 500 dependencies. The idea of needing to pay for a license means they have to stop building and get other people involved who may or may not approve, which may not be an option if they have a deadline. They will probably just try to find some work around to avoid this.

I wonder if a better approach is to move hundreds of libraries into some kind of joint bundle (a humble bundle). Let companies buy access to them all with one procurement, and also you’ll have more negotiating power and pull if you have a bigger group.

Make a "pro" version that costs money.

Why do you want to monetize it?

You could create a donation page. If no one wants to donate it is probably because there isn't a perceived benefit of the software.

Yeah, that was always a bad argument. The truth is it will always fail in the transitional step where the state owns everything. People in power do not want to give up that power, so it inevitably leads to dictatorship followed by eventual collapse.

This is the most interesting thing I've seen on the subject of motivation, and one of the most interesting videos I've ever watched. 10 minutes. Do it y'all.

https://www.youtube.com/watch?v=u6XAPnuFjJc

It explains so much of why I happy or unhappy at jobs, even if being paid far more for less work. Making more money does not equate to satisfaction or better productivity. It explains why we work for free, the very subject at hand. There's much I'm unhappy about working at Lowe's, quite the pay cut from my IT career and it's physically beating my old ass, but I have the 3 things he talks about in the video, and it turns out, those things are gold.

Germany is currently paying out a little through the "sovereign tech fund"

https://www.sovereign.tech/tech

The frustrating thing working in a big company is wanting to pay for something that costs 0.0000001% of the company's annual revenue, but not being able to because big companies are always divided up in hundreds of small teams with their own budgets, and your boss is already over-budget for the quarter because the team's cloud bill was 20% higher than predicted.

This is, of course, working exactly as designed.

That's not how a capitalist system works. In capitalism, one can only do things for personal gain. Anything else will be lost effort. Even if a company gives out free stuff, that's ultimately for their own gain

https://www.linuxfoundation.org/about/members They are hiding here.

There is so much unpaid labor that big tech depends on. If they had to fairly pay for all that work through donations or otherwise they would go bankrupt, every single on of them. Big tech grew so massive because on open source, but it also helped open source grow. big tech will also die because they are increasingly just a leech-like middleman that just sits upon a mountain of free work and whose relative sliver of code contribution in comparison to the total code in a product is getting smaller and smaller and big tech is therefore increasingly a burden and not a asset to societies, economies and other companies.

Governments should be funding the most popular open source software that the world relies on

profits of business have always been dependent on governments funding research and free work done by individuals to turn a profit. Open source is nothing new on this regard.

Exactly, that's why we need to convince governments to pay for FOSS.