I just got the new 2020 Roku Ultra, and have noticed something odd. When playing something with Dolby Vision (DV), my receiver shows color space of YCbCr 4:2:2 and pixel depth of 8 bits. I don't believe this is a valid Dolby Vision configuration. RGB with 8 bit and YCbCr 4:2:2 with 12 bits are valid DV outputs, but not YCbCr with 8 bits. In comparison, my Chromecast Ultra output DV with BT.2020 colorspace an 12 bit pixel depth.
Also, when browsing the Roku homepage, it outputs in YCbCr 4:2:2 with 12 bits (but no DV because I have the always HDR set to Off), so I know the device can output that configuration.