XER10 is problematic for home network use...

I've spent the last 4.5 hours on the phone with tech support and still don't have any clear idea how to work around this, because they literally don't know how to answer these types of questions.  Spoke to 3 people and got the same "follow this link to put in bridge mode".  Problem is, from what I've come to learn, is that the XER10 apparently doesn't have a bridge mode. So who at Comcast do I have to payoff to allow the ONT to go straight to my UniFi UDM Pro?  The only other option I have is to continue to deal with support after driving an hour to pick up a XB8 and dealing with bridge mode.  Wouldn't life just be easier if they allowed you to use the equipment you already have?