The date format codes are not universal. They are location dependent.

I see your location is Switzerland and wonder if in fact your date format codes are:

d = day
m = month
y = year

We can do some testing to find out.

Create these named formulas. These use Excel4 macro functions and will return the date format codes based on your regional settings.

Name: YearCode
Refers to: =INDEX(GET.WORKSPACE(37);19)

Name: MonthCode
Refers to: =INDEX(GET.WORKSPACE(37);20)

Name: DayCode
Refers to: =INDEX(GET.WORKSPACE(37);21)

Then, enter these formulas in some cells:

=YearCode
=MonthCode
=DayCode

Then, try to use those date format codes in the TEXT function.