Hi Sameer,
thank you for your answer.
I know that there is the possibility to work with the Column Engine. But in the upper right of the Expression Editor of the Calculated Column you can choose between "Column Engine" and "SQL". If you choose SQL, SQL Function will be suggested in the buttom instead of Column Engine Functions.
And you see: DAYS_BETWEEN is suggested. So I expected it to work.
Kind regards
Fabian