It would be great to help with solutions to climate change, equality, or mental health, etc. Perhaps I’m just not aware of it but it seems like most of these sort of things are primarily in the realm of other disciplines - humanities, politics, non-software eng fields. What are some ways software eng can meaningfully contribute?
Computers are everywhere today, and charities do work more efficiently thanks to specialised software as well.
In the UK, for example, you can find a job at a charity on https://www.charityjob.co.uk/, and some need software engineers/web developers.
If you want more of technology-focused companies, one example that comes to my mind is a Little Ripper, life-saving drone https://thelittleripper.com.au/.
Another one, online GP https://www.babylonhealth.com/
They are out there, but sadly they don't have the same reach as corporations. Another debatable reason: to save our planet, all of us need to take action and software can't help here.
Additionally, there are enterprise software companies out there that enable the kind of volunteer matching and donation matching that I mentioned above. This software usually falls into the category of "workplace giving". Working on software like this could provide some of the goodness hit that you're looking for.
I work primarily on projects for Health & Human Services and definitely feel like I'm doing much more good in the world as a civil servant than I was as at a FAANG.