Take a moment, pause and then think about the concept of a VLAN (a
Virtual LAN).
As it is being used, it has two end-points. The first end-point is way "north" ("upstream") of you. The second end-point should be defined in your modem. No other equipment should know (or needs to know) about that VLAN, with Ethernet frames tagged 101.
Looking a little deeper, but still simplistically, the port on your ZyXEL device (the LAN1 port) is a portal for the ingress and egress of Ethernet frames. (Your local device, producing and consuming Ethernet frames, is the Ubiquiti Edgerouter.) Those frames (with a 101 tag) are then transferred over the VDSL2 (ITU-T G.993.2) link to the cabinet based DSLAM and, keeping things simple, further "north" ("upstream") to the other end-point of the VLAN, where the tags are then removed, leaving the stream of Ethernet frames to be consumed and produced by a device (logically the mirror image of your Edgerouter) in ISP/CP land.