For anyone who wants to donate to directly support Let's Encrypt, its parent entity is Internet Security Research Group, a 501(c)(3) charitable entity. You can make donations to ISRG at https://letsencrypt.org/donate/. Businesses can also become formally recognized sponsors at https://letsencrypt.org/become-a-sponsor/ (though that might not match the giving patterns or preferences of DuckDuckGo).

Thanks to DuckDuckGo for all of its donations this year and other years.