Logon Trigger not firing on read only standby database

OS: RHEL8

DB: Oracle EE 19.14.0.0

I have a logon trigger for my primary database. For the purposes of this discussion, lets just say it writes a message to the alert.log using dbms_system.ksdwrt.

I have a primary database open for connections. When somebody logs onto the database, the trigger fires and writes an entry to the alert.log.

I also have a standby database open read only using Active Data Guard. When the same user logs onto the read only standby database, no message gets written to the alert.log.

I believe the logon trigger is not firing on the read only standby database, but I can't find any reference to whether that is expected behavior or not.