I do have a demo as part of my optimizer related workshops that shows the restriction / limitation of DBMS_STATS not supporting extended statistics on virtual columns / group of expressions, so for example the combination of both expressions and column groups, like ((TRUNC(COL1)), (TRUNC(COL2))).
Surprisingly, when following a certain sequence of operation, this starts working (to some degree) from 12.2.0.1 on.