EDIT: I mean directly from the box, NO casting from a phone or tablet.
All their channels are on-air via Livestream - here's an example - but a couple of years ago the parent company Vimeo discontinued their app for Roku, they just digitally yanked it out of our streaming boxes.
Sadly I can not comment on the current state of roku development patterns. I gave up on them a few years ago. There is no official twitch app for roku either, so I started investing and found a Github repo that you could compile and sideload your own from. After mine was remotely removed from my devices a few times I decided to move on from the roku bureaucracy.
I had watched for year as services and channels came an went from Roku. Reminded me when Direct TV was having problems with certain stations demanding more money to be on the service. Roku is not an open platform for developers. It a corporate advertising platform.
Sounds like conspiracy talk, and I don't mean it like that. However I honestly don't think of Roku as the small friendly platform it started as anymore. It has changed and I don't think it is for the better.
Sometimes their programming is arid, like sermons or political town halls, but sometimes... often in fact, mostly late-night... the NYC local program creators lets its' hair down and freak fully on, I cannot believe what I am seeing and hearing, from the garish to the sublime, from the mundane to the avant-garde, and everything in between.