Just quick and dirty notes on some references.
Notice that the Thread # is 0 for the SRL’s. Resist the temptation to explicitly assign the SRL to a specific thread. If you are using Oracle RAC, a SRL with with Thread # of 0 can be used by any primary instance, any thread from the primary.
https://community.oracle.com/docs/DOC-1007036
Warning: standby redo logs not configured for thread <n> on <db_unique_name> (Doc ID 1956103.1)
Bug 14674237 – VALIDATE DATABASE from BROKER incorrectly reports on standby redo log files (Doc ID 14674237.8)
Warning: standby redo logs not configured for thread 0 on DATABASE
https://jameshuangsj.wordpress.com/2018/01/17/warning-standby-redo-logs-not-configured-for-thread-0-on-database/
When run “Validate Database” DGML command, get “Warning: standby redo logs not configured for thread 0 ” and “Insufficient SRLs” warnings on 12.1.0.2 database with “Database Patch Set Update : 12.1.0.2.170814 (26609783)”.
Oracle 12c DataGuard – Insufficient SRLs reported by DGMGRL VALIDATE DATABASE VERBOSE
https://blog.dbi-services.com/oracle-12c-dataguard-insufficient-srls-reported-by-dgmgrl-validate-database-verbose/
Even on a single instance, use the thread number in your create Standby Redo Log statement.