When running the following statement...
MERGE INTO table1 t1
USING sys.table2@dblink t2
ON (t1.col1 = t2.col1)
WHEN MATCHED
THEN
UPDATE SET t1.col2 = t2.col2
WHEN NOT MATCHED
THEN
INSERT ( t1.col1, t1.col2)
VALUES (t2.col1, t2.col2);
it is failing on the "t2" assignment to the sys.table2@dblink t2 table. It's throwing a syntax error
"Found `t2`: Expecting: ("
It doesn't like the dblink in the merge. This is not a problem in v12.10.
For some users it will throw an error, not allowing the statement to be executed. For other users it will just have the row marked in the gutter as having an error and the user is able to execute it.