When AT&T was using an ONT + Gateway there were ways to circumvent traffic going through their Gateway while still allowing the Gateway to talk to the ONT and unlock it. But they've transitioned to deploying a single box (BGW320s) that are a single unit.
You can still put the Gateway into passthrough mode and disable it's features.
He's got the two box solution, so I guess my memory served me correctly about the workaround and I'll try to check the discord in the sibling comment for more help, thanks!
You can still put the Gateway into passthrough mode and disable it's features.