Ah. missed the compat level because I changed the it to version 10 in the debian/control file. Next upload will have debian/compat of 10, and debian/control has "Build-Depends: debhelper (>= 10.0.0), binutils (>= 2.28.0), autotools-dev (>= 20161112.1)"
So now to talk about the dpkg-shlibdeps warnings. The Debian package installs the binaries (libmux.so and others) under usr/lib/tinymux/game/bin, and then for a specific game, one runs tinymux-install script to install a symbolic link into the current directory. The install scripts creates a minimal game tree from which to start a game. So, the server itself never runs directly from the /usr/lib/tinymux/game/bin directory. That's why it works despite these warnings.
But, I agree that suppressing or fixing these warning is a good thing except that nothing I Google and no man pages I read describe how to actually go about doing this. dh_makeshlibs does run but it isn't picking up the location where libmux.so is placed. The man page for dh_shlibdeps describes this exact scenario and suggests to run dh_makeshlibs first as the obvious solution, but that is already happening and it doesn't work. Solutions point to using override_dh_shlibdeps, but then, I need to pass it all the right arguments and I think the problem is really dh_makeshlibs. Nothing I've found describes how dh_makeshlibs does its job or how to control it. Sorry, but I'm always at a loss for how to control these builds.