Ok, so this was the problem:
you must add P2D on the size method
size(500, 500, P2D) fixes the problem.
Now looking to understand the warnings generated by that:
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by com.jogamp.common.os.NativeLibrary$3 (file:/C:/Users/atadres/Desktop/processing-3.5.4/processing-3.5.4/core/library/gluegen-rt.jar) to method java.lang.ClassLoader.findLibrary(java.lang.String)
WARNING: Please consider reporting this to the maintainers of com.jogamp.common.os.NativeLibrary$3
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release