DIAGNOSIS This is typically caused by an automatic software update check or a malfunction in the Android TV's Quick Start feature. The TV wakes from standby to check for updates or refresh app data.
FIX Disable automatic updates. Go to Settings > System > About > Software update. Set Automatically check for update to Off. Next, disable Quick Start. Go to Settings > System > Power & Energy > Quick Start. Set it to Off. The TV will take longer to boot from a cold state but will not wake autonomously.
IF THAT DIDN'T WORK An external device connected via HDMI-CEC (Bravia Sync) may be sending a wake-up signal. Turn off CEC on all connected devices individually (e.g., cable box, game console). On the TV, go to Settings > Channels & Inputs > External Inputs > Bravia Sync settings. Set Device auto power off to Off. Set TV auto power on to Off.
HEADS UP If the TV is connected to a smart home system like Google Home, check for routines or commands that might be turning it on. Disable the link in the Google Home app as a test.