[Karellen]

https://www.debian.org/donations

> The easiest method of donating to Debian is via PayPal to Software in the Public Interest, a non-profit organization that holds assets in trust for Debian.

https://www.spi-inc.org/

> Software in the Public Interest (SPI) is a non-profit corporation registered in the state of New York founded to act as a fiscal sponsor for organizations that develop open source software and hardware. Our mission is to help substantial and significant open source projects

Edit: But also, freexian

https://www.freexian.com/lts/debian/

> To achieve the 5 years of support, and properly cover all Debian packages, Freexian organizes a corporate sponsorship campaign with the goal of funding the work of multiple Debian contributors who are established as independent workers.

> If you are not yet convinced, here are seven reasons why you should help fund the Debian Long Term Support initiative (LTS):