vlcj: libvlc_instance_t not accessible after module creation

Question

I have recently migrated my project from Java8 to Java17. I wanted to try out the module system and added a module-info.java to my existing Eclipse project. As it caused several issues, I decided to revert back the change and to proceed without declaring modules. I deleted the file, but now I am getting compile errors. It is stated that LibX11 and libvlc_instance_t cannot be resolved to be a type and that they are not accessible. Why is that? It was working fine before. It seems that adding and removing the module-info.java has somehow messed up my configuration.

I need to access libvlc_instance_t because I need to subclass MediaPlayer, which requires a reference to libvlc_instance_t in the constructor. If libvlc_instance_t is really not meant to be used, how can I solve this? Thank you!