I have zero experience with Dolby Vision. The LG set I just bought does support it, but my AVR doesn't. From what I've heard from other posters on other forums, DV can be touchy with some Sony products, although I believe that was mostly devices that were from 2017 or before. Both of yours appear to be more recent, so I wouldn't expect them to have issues.
It's possible your HDMI cable isn't satisfying the bandwidth requirement for 4K/60 HDR. It has to be a certified 18 Gbps cable to support that requirement. So that's the first thing I'd try. That tripped me up when I replaced my Roku 4 with the original Ultra. My cable worked fine on the 4, but would not work with the Ultra at 4K/60.
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What's worse is that if I force the ROKU to 4K without DV, the next time I turn it on, it reverts to 1080p with DV. I can set it back each time I turn it on, but that's just on the borderline of unusability.
Same here with my 2016 LG OLED E65. All LG OLED's prior to 2018 or 2017 only supported Dolby Vision 4K at 30hz. The Roku Ultra 4800R is forcing me to Dolby Vision at 1080p/60hz, and the picture is worse than regular 4K. I have set mine manually to 4K/60hz and not sure if it's resetting back to DV though. I do wish that they would just quickly fix Dolby Vision to support 4K at 30hz, which is still better than HDR10 for movies, etc.