Oracle Database 19.3 on Windows: Howto impdp or expdp from a UNC path in Windows?
You may find the below interesting: 

http://christian-gohmann.de/2019/05/19/symbolic-links-in-directory-objects-not-permitted-with-oracle-18c-19c/

Long story short, I had the same issue, then after setting the parameter below and restarting the database, Data Pump was able to use the network share.

ALTER SYSTEM SET "_disable_directory_link_check" = TRUE SCOPE=SPFILE;