Hello @Alexandru_Paul_Csiki, welcome to the forum.
There was a similar question couple of months back, on this forum. Here is the link to it. In that case, it was the query used with mongodump , but the syntax for the query option is same (I think). Please check the post and tell us if it helped.
Mongodump –query not able to filter using timestamp
Also, include a sample document showing the field(s) used in the query and the operating system you are working with.