Thank you for your fast answer!!
So Teltonika made two mistakes:
1) "This chapter is a summary of the UPnP function in RUT Routers" - makes me think this is valid for any RUT (https://wiki.teltonika.lt/view/UPNP)
2) RUT240 poduct site: features, chapter "Network: ".... PPPoE, UPNP, SSH, DHCP..." ( https://teltonika.lt/de/product/rut240/#features )
(For the handling of axis products I will have to fight my way through, one of their install info only refers to UPnP (because it's so easy) and they don't specify any port to open no more ... but this is off topic ... the cameras are attaced to a harddisk recorder axis companion wich also has routing capabilities, the RUT240 is the Gateway to G4 mobile internet ...)
thanks again & bye