This looks like it could be a UI/theme-related issue, especially because the Date Picker works correctly on a normal page but behaves differently inside a popup.
Could you please share a bit more information?
A common cause for this type of issue is CSS affecting the Date Picker overlay (z-index, overflow, or popup container styling), which can make the calendar close immediately after selecting a date.
If possible, also check the browser console for any JavaScript errors when selecting the date.
Could you please add the screenshot of existing issue. so that i can help you with this