Calendar and date display format

Is there a way to display days that are less than 10 with two digits, like 01, 02 etc?

are you looking for this on GNOME Topbar or in some other Apps/ areas?

No, I’m looking for a way to change it on the Calendar Widget:

No there isn’t.______

Have you looked at strftime()?

%d|
The day of the month as a decimal number (range |01| through |31|).

IIUC the calender widget takes %d from $locale -c -k LC_TIME
you then can modify or create a LC_TIME on your local computer

https://gitlab.gnome.org/GNOME/gtk/-/blob/master/gtk/gtkcalendar.c#L1502