Nobody is funding Debian. Never have. It's all volunteers.

And if you count the volunteer time, it dwarfs the paid time. So the biggest funder in real terms is the unpaid volunteer community. By far.

In fiat terms, Red Hat has been the biggest corpo distro for decades, so they probably still spend the most dollars. But maybe you're only counting paid kernel development time, or donations to the Linux foundation, or money spent on some subset of Linux distros.

All I know is that you are missing the majority of the contributions if you are only following the money.