iOS on a Mac Mini, current Core version
I have custom remotes on an iPhone and iPad, with a panel that displays the Roon web display in a WebView control. Or at least it used to - After a recent Roon update, perhaps when the port number changed to 9330, the view just shows the Roon logo with a little question mark icon. One iOS device is on the latest 15.5 version, and the other is back on 12 something, so it doesn’t look iOS dependent.
The Roon app shows that the devices are connected in the Displays section of settings.