Hello,
actually, analyzing, it seems to me that the clock, after some time, leaves the watchface (which is an service) invisible and starts another service, which is the watchface in standby (or another name ...).
I checked this by viewing the source code of a watchface in java, but my knowledge did not allow me to go much further ... if you want to take a look at the code, the link is
https://github.com/manuel-alvarez-alvarez/malvarez-watchface
But, I will verify the SetScreenBrightness(0) option.
Thanks