Maven-publish plugin said to be "incompatible" with Gradle 5.0

On ./gradlew build I get

Deprecated Gradle features were used in this build, making it incompatible with Gradle 5.0.

… but it also says BUILD SUCCESSFUL. I’m not sure what
this means… NB this attempt to use “maven-publish” is related to my previous question: I’m wondering whether or how I can use a “local Maven repository” (whatever that is) to allow versions of modules (classes, etc.) from one project to be available to others as dependencies (which will also pull in their own dependencies if missing)…

It’s not maven-publish that’s incompatible. It means something in your buildscripts or a plugin did something that will not works in gradle 5.0+
Run the build with ./gradle build -warning-mode=all and you will get an warning message at the end of the build explaining what the actual error is.