Search notes:

$ORACLE_HOME/install/orabasetab

The orabasetab file stores the location directories that are based on $ORACLE_HOME, ORACLE_BASE, ORACLE_BASE_HOME and ORACLE_BASE_CONFIG.

$ cat $ORACLE_HOME/install/orabasetab
/u01/app/oracle/product/21.0.0/dbhome_1:/u01/app/oracle/OraDB21Home1:Y: