The quick answer

Yes, the Xiaomi, Poco, Redmi Always on Display AOD really does switch off after 10 seconds! It's a 'MIUI optimisation'.

How to make it stay on?

Two steps, the first is to activate 'Developer mode' in the settings, the second is to then use the developer option to deactivate the 'MIUI optimisations'.

To activate the developer mode:

Settings, About phone then tap the 'MIUI version' a few times and a message will pop up to tell you developer mode is now active.

To deactivate MIUI optimisations:

Settings, Additional settings, then Developer options.
Scroll right down to the bottom and a few options up is 'Reset to default values'. Tap it a few times and several further options will appear,. Take the 'turn off MIUI optimizations.

The Always on display will now operate all the time.

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