On March 2020, chromium launched a proposal to deprecate browser native dialogs alert(), confirm(), and prompt(), when the code creating them runs embedded in a frame and was loaded from a different origin than the host page.
As a result, once chrome rolls out this, customers rendering Liferay in a cross-domain iframe would not get browser-native dialogs rendered.
So, We decided to implement replacements for these functions called openAlertModal and openConfirmModal. They will behave as native dialogs unless you enable custom implementation under Instance Settings -> Custom Dialogs. It will render our fallback dialogs implemented using ClayModal/openModal API instead of the native ones.