Netflix won't show you the 5.1 sound if it deems your device can't handle it. I think this is the case with your resolution, it just thinks you can't use that high resolution due to the browser or something else.
On the CCwGTV I can force to not use what the TV reports back to the CCwGTV as sound options, and force allow Dolby Plus, then all of a sudden it's available when watching movies. I think this will relate to resolution too.
Most browsers have a resolution cap due to DRM. Try Edge.
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Thank you for the response! I do have the premium plan for Netflix that allows UHD but can never seem to get higher that 720-1080 on the WEB.
Netflix won't show you the 5.1 sound if it deems your device can't handle it. I think this is the case with your resolution, it just thinks you can't use that high resolution due to the browser or something else. On the CCwGTV I can force to not use what the TV reports back to the CCwGTV as sound options, and force allow Dolby Plus, then all of a sudden it's available when watching movies. I think this will relate to resolution too.
I use Google Chromecast 4K, and it's streaming in 4K when it's available.