I am guessing you are using cmake >= 3.16 so it allows you to run, but since the project does not have a cmake minimum, for others using cmake < 3.16 the build will break. This warning highlights it, so you inform your contributor they need cmake 3.16 before running into the hard fail in FindKF5.
TLDR; If you use FindKF5, you should add cmake minimal version 3.16. -- Méven
