Can I connect an ASUS RT-AX55 V2 directly to my Xfinity Fiber ONT/ONU without the XB7?

I have Xfinity fiber service with an ONT/ONU and an XB7 gateway. I am trying to completely remove the XB7 from my setup and connect my own ASUS RT-AX55 V2 router directly to the Ethernet port of the ONT/ONU.

My current results are:

ONT/ONU → XB7: Internet works normally.

ONT/ONU → XB7 in Bridge Mode → ASUS RT-AX55 V2: The ASUS receives a WAN IP and internet works.

ONT/ONU → ASUS RT-AX55 V2 directly: The ASUS does not receive a WAN IP.

I have already spoken with Xfinity support online and also had an Xfinity technician come to my home. The technician contacted internal support and was told that the ASUS RT-AX55 V2 was “not compatible” with this configuration. However, no one has been able to explain what specifically makes it incompatible.

I am not asking how to use the XB7 in Bridge Mode. My goal is to remove the XB7 entirely and use:

ONT/ONU → ASUS RT-AX55 V2

Can an Xfinity employee please clarify whether this configuration is supported on my fiber service?

If it is supported, does the ASUS WAN MAC address need to be registered or provisioned on the account, or is there another requirement such as DHCP provisioning, VLAN configuration, or another authentication method?

If it is not supported, I would appreciate a technical explanation of what specifically requires the XB7 to remain connected.

I would like to understand whether this is an actual hardware compatibility limitation or simply an account/provisioning restriction.