Hi
It is not possible to keep the display awake without ongoing interactions with it.
When waking the screen by raising your wrist (with that setting enabled), the screen will stay awake for a few seconds without further interaction.
The display can also be set to stay awake for up to either 15 or 70 seconds. This applies when the screen is tapped on to wake it or when it is tapped on after being woken by raising your wrist.
To set your preferred wake duration when tapping the screen:
On your iPhone, in the Watch app, go to: My Watch (tab) > General > Wake Screen - under On Tap, select Wake for 15 or 70 Seconds.
It is normal for the display to sleep if your wrist is lowered within that time.
It is also not possible to keep the display permanently awake during charging.
If you would like to submit a feature request to Apple, then you can do so here:
Feedback - Apple Watch - Apple
You are not talking to Apple here - this is a user-based technical support community.