The ABSO module will activate the brake lights whenever the deceleration rate exceeds the threshold of deceleration speed, whether braking is done through the regeneration system or the main braking system has been engaged to stop the vehicle.
If the battery is at MAX charge (about 95%?), the REGEN may be disabled to prevent an over-charging condition.
In the case of the video however, the Ioniq 5 in ipedal mode (the mode that allows one pedal driving) you have to have your foot completely off the gas for the brake lights to engage. The example in the Ioniq, he decelerates from 60 to 0 and the brake lights only came on right as he was stopping. He cites that the 2016 Bolt have an accelerometer in it to account for this so that the brake lights come on.
In the 4xe video, a weird phenomenon is going one where the brake lights come on, but not when you're rolling down hill coming to a stop.