Casting works on smart tube by pairing it with revanced or official YouTube app via the remote control settings. After pairing, the cast button will send video to your smart tube app on your tv. The caveat is smart tube must be running first, it won't be automatically launched if it's not running like the official YouTube app when you hit the cast button.
Is this "set and forget" (I do it once and it stays connected for years), or do I have to re-connect after e.g. every TV restart? I assume it's the earlier, which isn't good enough for me.
Oh, that's much better than I expected! In the past I tried the YouTube-in-browser version of this, and it disconnected when closing the tab, so I assumed it would be similar. Thank you for the heads-up!