I saw your video. Thanks for posting that. You might be overloading the graphics capability of your phone. You have scaling going on, for sure. Are there any color effects added? What is the frame size and codec of the original clip? Let me know. Perhaps I can make some suggestions for you. Hope to help.
I assume it's h264. Idk what the r5 exports to and I can't tell from my phone. I have a pixel 7 pro. It would be unfortunate for a current gen flagship phone to be having export problems.