Why does my LG TV turn on after I unplug the Mac and open its lid?

Automatic LG webOS power control can send a network wake command when the Mac wakes, even if you have just unplugged the video connection. Enable Recheck connection on wake to have BetterDisplay check the associated display before sending that wake command.

Open Settings > Displays > [TV] > Device Control > Configure LG webOS Smart Device… and find Power Control. With Enable power control and Allow powering the device on enabled, turn on Recheck connection on wake. BetterDisplay waits for its configured wake and display-configuration delays, then skips power-on if the associated display is no longer detected as connected.

This option is off by default for a reason: some sleeping TVs do not expose a detectable video connection until a network wake command has already reached them. If enabling the check prevents your connected TV from waking, turn it off again. You can instead disable Allow powering the device on and wake the TV manually when needed.

The check applies to system-wake handling. If you configured Third pass WOL attempt delay, that extra delayed attempt does not perform another connection check after it has been scheduled. Leave it blank or zero unless you need the retry. Other TV or HDMI-CEC automation can also affect power behavior. See LG webOS power settings for the related options.