There's an established organization called Open Collective that can let you support various open source software projects, with the organization acting as a legal and fiscal sponsor. It's not a 501c3 but it is a 501c6.

I use the platform to support tools I like or use, like Nuxt or Tabula: https://opencollective.com/nuxtjs

You can also support some groups that use open data philosophies or methods but aren't necessarily or primarily building software, like ArchiveTeam: https://opencollective.com/archiveteam

afaik, it depends on if the org you're donating to is a registered tax-deductible non-profit. I've personally never been able to deduct donations to individual open source maintainers, even if the donation was in the thousands, but maybe I just need a new accountant.