Still recommend that you show your ( printed ) TDAC together with your passport, so The Immigration Officer don’t get the idea you trying to hide something.
I was moved to fast track, because I had the QR and passport ready in my hand.
I talk about my experiences entering Thailand with / without TDAC last week.
So no need to repete to me, how it is done. Adress that to the OP.
I, with a printed QR code and passport in hand, was waved through Immigration in 10 minutes, where as the person sitting next to on the plane, ended up i 3 long queues, ending taking an hour, because didn’t do TDAC before arriving in Thailand.
Because if you get denied at Immigration, the airline are responsible for removing you from Thailand, and they may not have free seats on their flights out, and then they have to pay a hefty fine.
That’s why some Airlines will deny you to check-in if you can’t show TDAC at check-in.