Thanks for the notes here. There are many factors that can contribute to buffering behavior while streaming. Available bandwidth from your ISP, your wireless network connection quality, the specific channel/service's content delivery systems or servers, peak usage times, etc.
In general, we'd recommend starting here: https://support.roku.com/article/213122277-tips-for-improving-the-wireless-connection-to-your-roku-s...
Changing the wireless broadcast channel on your wireless router can often help improve your wireless connection and device performance by reducing wireless interference from nearby networks that may be using the same wireless broadcast channel. Channels 1, 6, and 11 are the most commonly selected by default. Contact your ISP or wireless router manufacturer for more help making this type of adjustment.
Also, former internal development options that may have been available in 'secret screens' are not functions that have ever been supported by use for consumers, and were purely for developmental purposes. The bitrate option you're referring to did not apply to all channels or use-cases, and was intended as a diagnostic tool for very specific use cases. If you are looking to limit streaming quality, this would either need to be in done in any specific channel or service's own settings, such as Netflix offers, or on your router by limiting the amount of bandwidth that is supplied to your Roku device. Your ISP or wireless router manufacturer would need to assist you in making these types of adjustments.
(In fact, I implemented the bitrate override screen and the underlying functionality.)
If the channel provides multiple nonadaptive streams at different bitrates, the firmware should pick a stream that matches your network bandwidth. If the channel only provides streams that are faster than your network, then changing the target bitrate isn't going to help anyway, since there's no stream that you can play. The only time it will help is when your network bandwidth fluctuates significantly, so that the firmware doesn't have a good idea of your actual bandwidth at the time you start the stream.