Ok, i found a way to show this errors, but i dont like the way it is working...
under Technology -> Net Names -> Check Same Net.
this throws a lot of unneccessary DRC
as a feature request: i would like to have a general structure rule for a whole layer. for example check layer top and dont allow structures smaller than 0.1mm for example. not between this and that and all types cross checking. as a result i can export a gerber and know that layer xy has no smaller structure than 0.1mm. thats the important thing for DFM as the manufacturer cannot produce the stencils and stuff if structures are too small.