Alternatively, instead of mvn jetty:run, use this command without the need to set MAVEN_OPTS:

mvnDebug jetty:run

Here's the reference.

In my case, I am using VS Code. When I run the command, the terminal would only show:

Preparing to execute Maven in debug mode
Listening for transport dt_socket at address: 8000

and wait until I click the Start Debugging button (after adding and the corresponding configuration in launch.json and selecting it)

Below is the configuration I used, just in case.

{
    "type": "java",
    "name": "Attach to Remote",
    "request": "attach",
    "hostName": "localhost",
    "port": 8000,
    "projectName": "your-project-name"  // Optional: Replace with your project name
}