Connect third-party router directly to ONU

I have Xfinity fiber service, and have been wanting to use my own third-party ASUS router with my ONU. I saw this article that outlines how I can plug the router directly into the ONU without any Xfinity gateway. I also called ahead of time to confirm my area supports this setup: https://www.xfinity.com/support/articles/member-owned-router-fiber-internet

I have contacted Xfinity customer support multiple times, but I've had an enormous amount of trouble trying to explain how it works, and it's been quite the headache. Many hours of dead-ends and confusion on the employee's part. I even had a technician come to my house, but they had just as much trouble as I have. I saw on another post that it has to do with the MACSec feature, blocking my own ASUS router, and that it can be fixed with a provision for the ONU. Is there someone that can help me set this up properly, so that I can plug my router directly into my ONU without any Xfinity equipment acting as a bridge or modem?

Here's the reply that mentions the MACSec issue: https://forums.xfinity.com/conversations/your-home-network/xer10-enable-bridge-mode/690fb39b0d657631dc8c5c1f?commentId=6a67e197b3ed1847a056b6b3&replyId=6a67e79ae768fbe286e14e47