Selector date range comparison in formulas

Hello everyone,

I'm trying to compare two dates from my gsheet data source (start date and End date) with the date from the date selector in looker studio. I want to display all the occurence that are between the two date of the selector. EG: if I select april (from 1st to 30th in the selector) I want all the occurence wher my start date and End date are matching.
Gemini provide me this solution to be put in a calculated field:

"(Start date <= END_DATE() OR Start date IS NULL) AND

(End date >= START_DATE() OR End date IS NULL)"

My issue is that I cannot save my formula (button is greyed) and the reason prompted is there is no argument provided. My start date and end date a highlighted in green and defined as date (calendar icon) and the bollean are regognised in purple (AND OR and IS NULL). The two formulas START_DATE() and END_DATE() stays in black and are not recognized. I selected my Start date as a dimension for the date range without success, and no date dimension either.


Any Idea how I can do this filter ?
Thanks

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