To allow netty to access the class, start java with the following option:
--add-opens java.base/jdk.internal.misc=ALL-UNNAMED
This opens the package jdk.internal.misc in module java.base to the unamed module.
See also the documentation for the java command, and this intro to the Java module system in general.
EDIT: For Netty to use its direct buffer optimizations, you also need to set
-Dio.netty.tryReflectionSetAccessible=true
There are a number of Netty issues on this subject, see e.g. netty/issues/7769