I believe: cmake (3.16.3-1~bpo9+1) stretch-backports; urgency=medium
should have been: cmake (3.16.3-1~bpo9+1) stretch-backports-sloppy; urgency=medium since buster has cmake (3.13.4-1) https://packages.debian.org/source/oldstable/cmake
I believe: cmake (3.16.3-1~bpo9+1) stretch-backports; urgency=medium
should have been: cmake (3.16.3-1~bpo9+1) stretch-backports-sloppy; urgency=medium since buster has cmake (3.13.4-1) https://packages.debian.org/source/oldstable/cmake