It exists (at least in enterprise edition):
SYS> describe sys.x$dbgalertext;
Name Null? Type
-------------------------------- -------- ----------------------
ADDR RAW(4)
INDX NUMBER
INST_ID NUMBER
ORIGINATING_TIMESTAMP TIMESTAMP(3) WITH TIME
ZONE
NORMALIZED_TIMESTAMP TIMESTAMP(3) WITH TIME
ZONE
ORGANIZATION_ID VARCHAR2(64)
COMPONENT_ID VARCHAR2(64)
HOST_ID VARCHAR2(64)
HOST_ADDRESS VARCHAR2(46)
MESSAGE_TYPE NUMBER
MESSAGE_LEVEL NUMBER
MESSAGE_ID VARCHAR2(64)
MESSAGE_GROUP VARCHAR2(64)
CLIENT_ID VARCHAR2(64)
MODULE_ID VARCHAR2(64)
PROCESS_ID VARCHAR2(32)
THREAD_ID VARCHAR2(64)
USER_ID VARCHAR2(64)
INSTANCE_ID VARCHAR2(64)
DETAILED_LOCATION VARCHAR2(160)
PROBLEM_KEY VARCHAR2(64)
UPSTREAM_COMP_ID VARCHAR2(100)
DOWNSTREAM_COMP_ID VARCHAR2(100)
EXECUTION_CONTEXT_ID VARCHAR2(100)
EXECUTION_CONTEXT_SEQUENCE NUMBER
ERROR_INSTANCE_ID NUMBER
ERROR_INSTANCE_SEQUENCE NUMBER
VERSION NUMBER
MESSAGE_TEXT VARCHAR2(2048)
MESSAGE_ARGUMENTS VARCHAR2(128)
SUPPLEMENTAL_ATTRIBUTES VARCHAR2(128)
SUPPLEMENTAL_DETAILS VARCHAR2(128)
PARTITION NUMBER
RECORD_ID NUMBER
SYS> @v
Oracle version: 11.2.0.4.181016 EE
@John, are you sure there is a view on it in 12.*? I didn't find it in my databases (there is only one on x$diag_ALERT_EXT).