I do know about the brake lights when the car slows with regen and with TACC.
In the past when I’ve used the turn signal partially depressed to change lanes under autopilot, then released before the lane change is complete, the car has abruptly changed direction in order to return to the original lane. Since that happened several times I started fully engaging the turn signal and then disengaging it once the lane change was complete. Has that abrupt behavior changed?
Once a front wheel is over the line into new lane there should be no bounce-back from cancelling the turn signal.