The charger... sparks..?
I just noticed that the charger sometimes makes some sparks when connecting or disconnecting it from the watch, and sometimes while charging it also makes a weird electrical buzzing noise, which you can hear in the video if you raise the volume enough.
I doubt this is intended behaviour, so I wonder if it's a design or manufacturing issue.
Either way I ruled out the issue being my chargers or cables, since I tried various combinations including high quality PD setups and normal low power charging and they all present the same behaviour.