This is a normal sbt project. You can compile code with sbt compile, run it with sbt run, and sbt console will start a Scala 3 REPL.
For more information on the sbt-dotty plugin, see the scala3-example-project.
install Metals plugin, then add your project to metals, create this launch json file
{
"version": "0.2.0",
"configurations": [{
"type": "scala",
"request": "launch",
// configuration name visible for the user
"name": "Launch Main",
// full name of the class to run
"mainClass": "some.package",
// optional arguments for the main class
"args": ["Arg1", "Arg2"],
// optional jvm properties to use
"jvmOptions": []
}]
}