I have a Roku Ultra 4670X (10.5.0 build 4208-46), LG 2020 CX TV, and Sonos Arc Soundbar. All was working fine since I got everything about a year ago but with what I can only assume is a recent auto-update, my Dolby Atmos has not worked for like a month. It just plays in HDR when I try from an app that should be able to play Dolby Atmos like Disney+. My AppleTV and the native LG OS Disney+ apps all play Dolby Atmos properly so settings on the TV are correct for my setup (HDMI ARC, eARC on, etc.) Roku audio settings also look correct - Audio mode is Auto, Streaming audio format is Dolby, and Digital output format is Auto, it's an older Roku so there's no Passthrough option but it is a Dolby Atmos model. Reset my Roku back to factory settings and still no dice.
Same issue here. 10.5 broke Atmos on my TCL R635 and Vizio M512a-H6. Both show "stereo" as the output after the TV is turned off, and back on. Only fix I've found it switch between Auto and Passthrough, or unplug and replug in the HDMI cable from soundbar or TV. Then it works again till the TV is turned off. Fix this 10.5 update please before I miss my return window to return my TV and soundbar.