On a 2019 Denali intellibeam was optional
TQ5 IntelliBeam, automatic high beam on/off
1 - Included and only available with (PDJ) Driver Alert Package II.
TQ5 and or PDJ rpo codes in the QR code or the build sheet would verify installation.. (a phone with a qr code reader app is needed --- and they QR doesn't have all the codes so it might be necessary to get the build sheet)
But, if the 'A' lights up on the dash, it would seem that intellibeam is both installed and operating.
If there isn't a button in the end of the blinker/headlight stalk it would seem a dealer visit is in order.
Fwiw, older sierra's with LED lights and intellibeam activated/deactivated the system by moving the blink stalk fore/aft, as is done to flash lights or engage high beams. It was difficult for many to use, so the button seems like a much better idea.