Review the following topics for information about using earlier Oracle Database releases with Oracle Grid Infrastructure 21c installations:

• General Restrictions for Using Earlier Oracle Database Releases
  Restrictions for using earlier Oracle Database releases with Oracle Grid Infrastructure 21c.
• Using ASMCA to Administer Disk Groups for Earlier Database Releases
  Use Oracle ASM Configuration Assistant (ASMCA) to create and modify disk groups when you install earlier Oracle databases and Oracle RAC databases on Oracle Grid Infrastructure installations.
• Using the Correct LSNRCTL Commands
  To administer Oracle Database 21c local and scan listeners using the lsnrctl command, set your $ORACLE_HOME environment variable to the path for the Oracle Grid Infrastructure home (Grid home).