Maven is one of the most common build tools in the JVM ecosystem and it also works with Scala through the scala-maven-plugin. The scalor-maven-plugin is not currently supported and requires a new plugin for bloop to be implemented.
The first time you open Metals in a new Maven workspace you will be prompted to import the build. Select "Import Build" to start the automatic installation. This will create all the needed Bloop config files. You should then be able to edit and compile your code utilizing all of the features.
Currently, all you need to run the manual installation is:
mvn ch.epfl.scala:maven-bloop_2.12:1.4.4-13-408f4d80:bloopInstall -DdownloadSources=true
If you choose this option though you should select "Don't show again" when Metals prompts to import the build.