Problem with saving date...30 days back

I set a variable ‘today’ with the function “Date and time” - interval minutes.
I entered the value in a form, creating a hidden field.
When I save the values in the database, the date is set to one month back.
2021-04-30 instead 2021-05-30
2021-05-01 instead 2021-05-31
I also tried to flag “UTC Time” but without change