Bluetooth has a delay for most codecs. Do not ask me how it is exactly done but there is a feedback to the application so that it delays audio to match video for the bluetooth delay. Some years ago a new Linux audio subsystem was developed, and this thing did not work at start but they fixed it later. From that time is my memory.

I haven't had that issue fortunately, I use mine to watch video all the time and have had no synchronization issues. Maybe later batches updated the BT modem?

that's not true, i use bluetooth headphones regularly to watch videos.