Sorry here’s a better tutorial. I might write one, it is interesting that they all suck in different ways.
https://starbeamrainbowlabs.com/blog/article.php?article=posts/237-WebDav-Nginx-Setup.html
The folder is defined by the “root” directive. Like with any other nginx setup.
Debian is KISS. Grab it and use, no need to overcomplicate things.