How do I find the files installed by a particular package? Where is the .deb file to look at?

I think there is an existing answer to your question (which isn’t How to get information about deb package archive?), but I can’t find it.

To list the contents of an installed package, use dpkg -L:

dpkg -L pulseaudio-module-bluetooth

If you want to list the contents of a package before installing it, install apt-file, then run apt update, and

apt-file list pulseaudio-module-bluetooth

will list the contents of the package without downloading it or installing it.

You can also view the contents of a package from its web page; look for “list of files” links at the bottom of the page.