Found this on h ttps://9to5mac.com/2019/09/24/apple-watch-series-5-always-on-display-turn-off/
So, I understand your app should stay visible if that's the last opened.
Here’s how Apple describes how the feature works:
Always On is turned on by default on Apple Watch Series 5. In this mode, the time is always visible, along with your watch face or the most recent active app. To preserve battery life, the display dims when your wrist is down or by a quick gesture of covering the display with your hand. A wrist raise or tap on the screen brings everything back at full brightness.
Yes, this is what current happens with most apps.
However, Apple's own Workouts and Breathe apps don't do this. They actually stay on the watch face but with a reduce update rate and no animations. As you can imagine, this is extremely useful while you are working out as it means you can just glance at your watch to get an idea of time remaining rather than raise your wrist (on a bike for instance).
I (and my apps users) want to know if it's possible for own workout apps able to opt into this behaviour.
I’m curious about this as well. I imagine we would need new APIs to tell the framework what to do with ui elements that updates more frequently then once per second (millisecond timers). Haven’t seen anything in the watchOS 6 docs. Hope they allow 3rd party workout apps to leverage the always on display soon!