NGOs jobs tend to be structured on topics as much as on functions, so making a shortlist of topical keywords might be helpful in the search to become aware of organizations. You should also look directly at organizations' staff lists, which are typically fairly open and have emails listed. One thing to be aware of is many nonprofits have tightly budgeted projects with specific needs, so getting your foot in the door on a less interesting project might be needed. Generalists can benefit here.
I know a few job sites that collect these kind of positions, some techy and some not:
https://greenjobs.greenjobsearch.org/
https://www.devex.com/jobs/search/
Last I will mention the nonprofit organization I work for - World Resources Institute (https://wri.org). We organize our work around seven global challenges: food, forests, water, the ocean, energy, climate, and cities. We do research, build data products and applications, organize partnerships. We help tackle some the largest questions related to how we collectively transition to a world where more than 9 billion humans have their food and energy needs met through fair economic and environmental systems.