Have you tried using your cell phone with the “official Roku app?”
You can configure the app to play the sound through your cell phone, a Bluetooth port on your cell phone, or the “USB-C” to audio out on your cell phone.
In the Official Roku mobile app there is a switch to toggle called “headphone mode”
Unfortunately, I cannot send you a picture of this Software switch, however, I can give you some instructions.
In the mobile app Link the app to your device. You can do that in a section marked “Devices” on my app, Devices” is located on the bottom of the screen. Select your Roku device that you wish to have connected to your cell phone for audio.
After selecting my Roku device, I select from the bottom of the screen, the icon named “remote” I get a working image of a roku remote control device.
You may check to see if the software remote is properly connecting to your device by using the left arrow right arrow home button, etc.
Presuming it is properly connected, in the upper right corner is a gear. Press the gear
Among other sub menus on the gear, you should see haptic feedback, Swipe, switch device, and “headphone mode.”
Select “headphone mode” And you may get some visual cues that your official Roku mobile app is now channeling the sound through your phone device.
Have your headphones connected to your phone device as you normally would for audio, and you should hear the sound of your Roku device. Depending on my headphones, and the type of phone I use, I can connect to the Headphone audio jack, Bluetooth into the phone, Or use the USB-C To Mini headphone Adapter connected to my USB-C on the phone.
Feel free to write back if these instructions do not work for you.
Or better yet let me know that these instructions do work for you!