Try this one:
E
Day name in weekTextTuesday
; Tue
u
Day number of week (1 = Monday, ..., 7 = Sunday)Number1
See documentation here:
https://docs.mendix.com/refguide/parse-and-format-date-function-calls#1-introduction and
https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/text/SimpleDateFormat.html
Regards,
Ronald