I would try all the steps that Dr. Stonedahl stated, but if that doesn't work make sure that your fxml file is mapped to the controller. It may not see the correct file and crash during runtime
Hmm... here are a few ideas to try:
Project -> Update Maven Project.
Right click on your project, and choose Build Path, and make sure that you are set to use the appropriate Java version. (Ideally everyone on your team should be using Java version 17, but if you don't have Java 17 or higher installed yet, then you might have to switch it to a lower version of Java to get it to run on your computer.)
