NBP12.3 application on JDK16/mac OS: Cannot load even default layout

NBP application using 12.3, JDK 16, runs fine on Linux.

On mac OS (Big Sur), I first got lots of relection-related exceptions from NbInstaller, e.g.:

java.lang.reflect.InaccessibleObjectException: Unable to make protected java.util.Enumeration java.lang.ClassLoader.findResources(java.lang.String) throws java.io.IOException accessible: module java.base does not "opens java.lang" to unnamed module @4ccc0db7
at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:357)
at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:297)
at java.base/java.lang.reflect.Method.checkCanSetAccessible(Method.java:199)
at java.base/java.lang.reflect.Method.setAccessible(Method.java:193)
[catch] at org.netbeans.Module.findResources(Module.java:567)
at org.netbeans.core.startup.NbInstaller.loadLayers(NbInstaller.java:605)
at org.netbeans.core.startup.NbInstaller.loadImpl(NbInstaller.java:332)
at org.netbeans.core.startup.NbInstaller.access$000(NbInstaller.java:77)
at org.netbeans.core.startup.NbInstaller$1.run(NbInstaller.java:322)
at org.openide.filesystems.FileUtil$2.run(FileUtil.java:413)

so I added 'J-illegal-access=permit' to default_options in etc/mgx_gui.conf.

Now, after completely removing the user_dir, I get

• a popup warning: 'Cannot load even default layout, using internally predefined configuration.'
• a NullPointerException related to FileObject.isValid()

UI window itself is opened, but remains empty. I'm attaching the full messages.log file,

any ideas would be greatly appreciated.