[Answered ]-Django FieldError: Unsupported lookup 'kategorie' for IntegerField or join on the field not permitted

Since cislo is an IntegerField, you can not join on this. you probably want to join on Mustek in reverse however, so:

kategorie = django_filters.CharFilter(
    label='Kategorie',
    field_name='ucet__mustek__kategorie__jmeno',
    lookup_expr='icontains',
)