My wife is having some hearing issues. I would really like to be able for her to use a headset to listen while the rest of the family listens to normal sound from the TV. I am willing to upgrade my Roku to whatever is needed.
I have the exact same issue and couldn't find a way to use the remote's headset jack without turning off the sound to the speakers. What I did to solve that is buy an HDMI audio extractor for $25 from Amazon and plug an extension cable into it for my headphones. You could also plug a Bluetooth transmitter into it to use with Bluetooth headphones.
In addition to the HDMI Audio Extractor [https://amzn.to/2XnqWxO] you'll also need a short HDMI cable [https://amzn.to/3bm89Lp] to use between the Roku box and the extractor. The Roku plugs into the Extractor's HDMI IN and the cable to the TV plugs into the HDMI OUT jack. Then plug the headset extension cord [https://amzn.to/2XpV6Az] (order whatever length you need) to reach her seat.
I bought that extractor 3 years ago and it's worked perfectly with my Roku. There are more choices now so you might find something better.
Not right that we should have to spend another $25 +. With Roku Ultra we had a way to use headphones plugged into the remote and push the audio up and down (up up down down and up up up down down down) to hear sound on head phones and speakers. Until Roku changed it on an upgrade. Many other Roku owners complained but we never got an answer.
I would think it would be a good selling point for Roku Ultra. Sound does not seem to be important to stream device or TV manufacturers, movie or tv show creators.
I currently have 3 Roku streaming devices, 1 Chromecast w/ Google Tv and 1 Amazon stick. Roku has been my favorite except for the audio issue.
It may not be "right" that Roku removed the function but at least it's a reasonably priced solution available right now that works until Roku restores the feature - if ever. The OP stated that he is even willing to spend money for a new Roku if need be and the HDMI audio extractor is a less costly solution.