According to every article I have read, if you have an iPhone with AOD, then Standby Mode is supposed to stay on, not go blank or turn off after 20 seconds. I don't know why else AOD would be mentioned specifically when discussing Standby Mode.
StandBy is a customizable Lock Screen mode in iOS 17 that activates only when an iPhone is positioned on its side (i.e. horizontally in landscape...
www.macrumors.com
Always-on display or bust
www.tomsguide.com
Now I am really curious why your 14 Pro with AOD enabled would not be staying on, when everything is saying it should be.
Hardware limitations, AFAIK. But from what you are describing, your 14 Pro in Standby Mode is behaving exactly like Standby Mode on my 13 Pro.