The following attampt to update a virtual column and demonstrates that doing so throws the error message ORA-54013: INSERT operation disallowed on virtual columns:
create table tq84_tab (
num_1 number,
num_2 number,
sum_ as (num_1 + num_2)
);
insert into tq84_tab values (1, 2, 3);
-- Cleaning up:
drop table tq84_tab;