Found the problem recording VDO with a separate Audio Line-in via adapter cable to 3.5mm jack. The built-in mic still picks up an audio signal as if nothing is attached to the jack. The cable is OK, switching TRS source to TRRS jack. Now thinking of buying another adapter cable, converting Line-in into USB-C charge socket at the bottom. But still doubt if it'll work. Bad luck when contacting Samsung rep. Nothing's useful.
Anyone tried it before or any thought on other alternatives? Thanks.