I understand that the Technical Debt metric became part of SonarQube after it was a plugin, but I would like to remove it from the dashboard completely, and only show other metr
Technical Debt is a core feature of SonarQube, so there's no reason why it should be possible to remove it from the main "pages" of the SonarQube web application.
If you want to hide this, you should first ask yourself why. Indeed, technical debt was not invented by SonarQube, this is a famous and widely spread concept that has been there for more than a decade. With this concept come good practices for software development. So again, trying to hide this in SonarQube is a bit weird.
Also, I highly discourage you to fork the code of SonarQube and write your own version just for this. Think 2 seconds how difficult it will be for you to maintain your fork, and I'm sure you will forget this idea as fast as it came to your mind.