I followed the docs and setup my .dockerignore like this:

# ignore everything
*
# but include all package.xml in any folder
!**/package.xml

However, these files are not added to the context as expected. Seems like ** doesn't work for inclusion?
Explicitly adding those files works as expected.

Docker version 20.10.7, build 20.10.7-0ubuntu1~20.04.1