Reports Filter

Hello, Mario,
 
Thank you for your kind feedback.
 
Currently, it is possible to hide the Report Filters box via CSS:

#fm-pivot-view .fm-fields-view .fm-popup-content .fm-list-wrap-pages {
    display: none;
}

Here is a JSFiddle example for illustration: https://jsfiddle.net/flexmonster/Lhxvmp7c/.
 
Also, it is possible to create your own Field List if a more custom approach is needed. 
Flexmonster provides a list of API calls that can be used for adding functionality to your Field List.
Please see the following thread for more details about how a custom Field List can be created: https://www.flexmonster.com/question/prevent-to-modify-fields-options/.
 
Feel free to reach out should any questions arise.
 
Kind regards,
Vera