if anyone want to access plc variables / symbols by an OPCUA client,
in current Version of CODESYS Raspberry Pi plc release
there is an OPCUA Server included in the CODESYS Pi plc runtime.
Check the following example (you need to install the CODESYS Pi Package to get this)
"c:\Users\<yourUserName>\CODESYS Control for Raspberry PI\22.214.171.124\OPCUA.project"