I have the same issue -
i have an iphone 13 pro as well, and just updated to ios 18.3;
the display stays on, especially when charging, either wired or wirelessly;
there is no Always On Display (AOD) toggle on the Display and Brightness page;
Auto-Lock is set for 2 minutes, but the screen stays on past that whether charging or not;
there are no Focus settings or Do Not Disturb settings set;
this has been happening for over 2 wks, even before the ios update, which i hoped would have included a toggle;
yes, all Apple sites say AOD started with iphone 14, but Apple has obviously allowed it to be on previous iphones, at least the 13 pro, most likely due to an ios update;
as for what SravanKrA posted, it is not an Auto Lock thing, and i am not using an app that prevents the Auto Lock - though good things to check.
thanks for any assistance 🙂