Given that almost everything written here is incorrect
Given your precision...I find your claim lacking.
My point was very to the point. It stands by itself why opus can't be considered for music tracks (re: album play and general single play - pick album gain for the gain to use and consider yourself lucky enough). You can start here.
as a mid-way point. If I come to find specifics in the source (it's been a long while since I looked at it) I may update here. jmvalin made a comment about fb2k doing something on its own. It's not in the opus spec. The spec (as I remember, and from reading Monty's very-old-now comments, about opus) looks like opus was intended for video/web play, not music album play. Microsoft in newer Windows 10 also looks to be using it only for web play (the browser, for audio of videos using opus).
Point is, if it can't do replay-gain right, it won't sound gapless when using RG. Not even close. Dismiss RG if you want. I can't. And what exactly is your problem with this now?