I live in Korea and got back from Thailand earlier this week. You don't need a QCODE and can do the manual form for it, but you need either the QCODE or manual form for entry. The QCODE only takes a minute now since most of the entries are not required or skipped (compared to the information required for it when I entered the country in May) so doing it in advance saved a lot of time compared to filling out the paper form. No one asked for the QCODE on the Thailand side on check in, but having it in advance allowed me to breeze right through after getting off the plane.