On the Telekom VDSL via modem, you have to be careful when setting up and set the VLAN tagging to "user-defined". After activating IPv6 with PPPoE, the Deco router assigned addresses via DHCP, which is practical for servers, but makes it easy to track everyone else. This can be corrected via "Internet connection type" and "Assigned type" to "SLAAC + Stateless DHCP"...