How do I make technical contributions to a meaningful cause

Problem is, not a lot of the world's big problems can be solved by setting up a web app with a CRUD back end.

Are you an expert in bioinformatics? Or perhaps a power systems engineer? Do you have deep experience with community organizing? Are you a reporter who can operate in conflict zones? Are you an entertainer with an audience big enough to lead a movement? Or maybe you're just a medical professional with an interest in working on neglected tropical diseases?

In a different vein you could find a company to work for more inline with your goals. Probably with a paycut.

https://80000hours.org/job-board/?role-type=engineering&role...

https://signal.org/workworkwork/

You are not going to change the world with this but you can contribute to neocities to promote an alternative web :

https://neocities.org/

https://github.com/neocities/neocities

https://helpwithcovid.com/

https://www.usdigitalresponse.org/

https://www.codeforamerica.org/

not sure about a group specifically about stopping fake news.

You can check catchafire.org. There's some opportunities there for technical volunteering

Look for jobs in NLP. There's a lot of interesting work to be done there. NLP for medical text s, NLP for intelligence encounter intelligence, NLP for lie detection. It's the space for your most likely to find work that is good