I just bought 70 inch Roku oon TV December 2020. I am having the same thing nothing is in front of my TV I have to be one foot directly pointing at sensor for my TV volume to work. I have three different remotes and it's the same thing. I believe it's something inside the sensor who would I talk to about getting that fixed?
We're sorry to hear about the issue you're experiencing – this is not what we aim for.
Have you tried contacting ONN Support to inquire further? I'd suggest starting there to see what options or suggestions they can provide. Each Roku TV manufacturer provides direct support and warranty services for their products running the Roku OS. Also, remotes for Roku TVs are manufactured directly by the TV manufacturer.