We're having this discussion in the OS 9 Release Notes
Last week Shawn asked some of us with 4620/4630/4640 devices to send him our device info so he could look into the issue of Night Mode disappearing. As someone in this thread noted, and I noted in the OS 9 thread, that support article for volume modes absolutely had the 4620 and 4630 in the chart. Well, guess what? They quietly revised the article yesterday to remove both of those models, and not a peep was heard from Shawn about it.
Night Mode worked just fine in the 4620/4630/4640 for a long time with OS 8.x, and yet mysteriously those devices are no longer able to support that with OS 9, but some cheap piece of junk like the Express can? LOL smooth move, Roku.
It has become painfully clear to me that Roku doesn't really care all that much about customers with slightly older devices. They've already got your money, so have little motivation to do the right thing. Those three 2016 models are as capable or more capable than any of the current models, including the 466x Ultra. The 4640 Ultra has the optical audio output, which they stripped out of the 2017-2018 models so they could lower the price.