I absolutely have a careful reading problem, but having said that, none of the repos linked from the update warning within the router software itself have the correct firmware. So if you are not on this forum, then you won’t have the GH link.
Just a heads up that it doesn't look like there's a specific release for DSL-AC68U, even though I'm getting update warnings (accidentally tried RT-AC68U and the update failed). Neither mirrors have the DSL models in their release directories. I'm assuming from the OP that the DSL models are...