Maven is one of the most common build tools in the JVM ecosystem and it also allows for using 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 workspace it prompts you to import the build. Select "Import build" to start automatic installation. This will create all the needed Bloop config files and all the features should work properly.
Currently, all you need to run the manual installation is:
mvn ch.epfl.scala:maven-bloop_2.12:1.4.3:bloopInstall -DdownloadSources=true
If you choose this option though you should select "Don't show again" when Metals prompts to import the build.