steps

Use JDK 8.

$ touch build.sbt
$ sbt -Dsbt.version=2.0.0-RC9

problem

$ sbt -Dsbt.version=2.0.0-RC9
[info] server was not detected. starting an instance
[error] failed to connect to server

This is somewhat confusing error since it hides the server error.

expectation

If the sbt runner script detects JDK lower than JDK 17, it should fail to launch sbt 2.0, and print out a message to stderr:

[error] sbt 2.x requires JDK 17 or above