MacOS - Calendar - start of the week

Good day, although I have adjusted the "first day of the week", this only appears to adjust the start of the week on the calendar itself, but does not adjust the popups when selecting dates in calendar events. Does anyone know how to make it that these little calendars also update the start of the week to match the calendar setting? I have attached an example; in the calendar one can see the start of the week is Monday, as per my preferences, but the new event popup window shows Sunday as the first day of the week.