Up until the last updates both Roku streaming devices and Roku TVs could be used with Smartview to mirror multimedia files as in with both video and audio but that's sadly no longer the case which has rendered the feature on all Roku devices and Roku TVs all but useless to the point they might as well remove the feature entirely.
And yes I've tried all the possible solutions to no avail and the multimedia files work fine on non Roku brands such as a Samsung TV I tested it on so its not originating from my smartphone but from Roku brand devices for absolute certain.
Until either a fix is made or the feature is permanently officially removed There's nothing to be done it simply doesn't work anymore. And before anyone says you can still view pictures on it nobody uses Smartview for that but to pipe in movies and TV shows that otherwise they wouldn't be able to.