From here I learned that etckeeper doesn't exclude files via the usual .gitignore file.
How can I view which directories and files are excluded from it? I'm using Debian 9.1 with KDE.
That's not what your link says. Etckeeper does use the usual
.gitignore file. The link is about the case when a file is added to
.gitignore when it's already registered. In that case, it remains tracked.