Database
[{"DateC":"06/03/2020"},{"DateC":"07/03/2020"},{"DateC":"03/03/2020"},{"DateC":"04/03/2020"},{"DateC":"05/03/2020"}]
Query
db.collection.find([{$expr:{$lte:[{$dateFromString:{dateString:"$DateC",format:"%d/%m/%Y"}},ISODate("2020-03-05T00:00:00.000Z")]}}])