Question about Zyxel G.Fast XMG3927 Bridge

I also bought the Zyxel XMG3927 (this is the version that is pre-configured in "Bridge Mode" and Wifi is *permanently* switched off) to replace the non-administrable modem from Wingo (Swisscom). The Zyxel VDSL modem now sits behind my XR500 Netgear router, so far so good because the internet works like this, wired as follows: -RJ11 cable (enclosed) with the RJ11 adapter (T83), also enclosed, connected to the DSL socket on the wall. -Router (XR500) WAN port connected with RJ45 Cat7 Ethernet cable to Zyxel RJ45 1Gbit *Switch* port - not to the WAN port of the Zyxel - this did NOT work for me. Now for my question: Apparently, when the Zyzel modem is in "Bridge Mode", the routing functions are of course switched off, but also the DHCP, Firewall and NAT. In my router (XR500) web interface, I now see that the Zyxel modem has got quite strange IPs: 100.77.165.166 and gateway 100.77.165.1. I can no longer access the Zyxel web interface under either IP. Is this "normal" in bridge mode? Or can I not access the 100.x from my local 10.0.0.0 network (DHCP of the XR500)?