[cmake] ParMETIS is not found even though PT-Scotch with parmetis bindings is installed

-- Could NOT find ParMETIS (missing: PARMETIS_DEPENDENCIES_FOUND) (Required is at least version "4.0")

On my Debian stable system with the following packages installed:

• libscotchparmetis-dev 6.0.6
• libscotchmetis-dev 6.0.6
• this one might interfere: libmetis5 (a dependency of dolphine, octave, etc.)

Metis is not found either! This limits the usability of parallel AMG.

Any clues? (There is nothing useful in CMakeFiles/CMakeError.log at all, besides an ARPACK message). Packages are found for DUNE 2.7!