I'm afraid I can't help you with a list of organisations to join, OP, but there are a few things I can think of to help in indirect ways. The unsexiest and most difficult but one of the most impactful is to strengthen unions by forming/joining them. Solidarity allows us as tech workers to gain agency in deciding which work we won't do and being empowered through collective action to push back against partnerships with the military-industrial complex. We can also use our skills and the rewards of our labour to contribute to and sponsor open-source projects regarding private, encrypted and decentralised communications which allow citizens, reporters, and aid workers (not always distinct groups) to avoid the kind of government censorship which accelerates genocide.

Besides that, I'm deeply interested in this thread and other responses, as someone who's been pondering the same thing for a long time. Where I've landed is that there might not be a special thing only I can do to help the current situation using the skills I have, but that the best thing I could do is use my financial security and work/life boundaries to do the unglamorous work of civic and political volunteering. It's possible that we can't hack our way out of this, but we can support the organisational efforts of others in other ways. Protest and community organising are still the most effective methods of arousing change, and while I would like to see more civil disobedience in the digital realm, it might be that the best a tech worker can do is go and march in the city square along with thousands of others.