You can't just build a private channel on ROKU
They have to allow it
Private only means its not in the channel store
ROKU has to provide the code to link the channel to their device
I would love to know what " certify" means
I checked both of my Roku's and I did find a few Private channels. A couple no longer worked. One called Endless Podcasts, I found most of what I listen to on Spotify for free. That is covered. Much of the rest are old TV shows & movie apps that are duplicated elsewhere or even on You Tube. Those I added in 2014/2015. I also have the NoWhereMan Archive channel that Roku dropped years ago. I could still use it if I had in on there. In checking that, most of the stuff is also on You Tube. So it looks like, at least in my case, I am not going to miss much. If there is no app on the Roku or Fire Stick, I can always cast anything on the Chromecast. The World of streaming has really changed since I got my first Roku LT in 2014. There were only maybe a 100 or so decent apps then. Now there are thousands. Having multiple streaming devices is an advantage and they are all pretty inexpensive.