Our users are picking up on this issue too.
An uneducated suggestion - If update messages contain topic ids, could these be filtered on client-side based on a user’s mute list? Caching the mute-list client-side would probably be okay as I expect most users probably only mute a small handful of topics (and in any case, we’d use a bounded cache of, say, 1000 most-recently-muted topic ids). No changes to message bus infrastructure required - it would be downstream of that.