It might be that my phone has a weird refresh rate strategy for saving battery life. I reported this to the OS developers, but they said they are unwilling to add edge to list of apps that forces 120Hz.
Edge worked perfectly when I force the system to always run at 120Hz (although ui animation was not as good as chrome's). I find this Frame Rate API from android developer site. Maybe it will be useful? Now that Edge Android Canary is already at target API 30, this might not be something difficult to add. And this might benefit other phone OSes that have (bad) battery-saving refresh rate strategy.
Here's a screenshot. You can see from the left corner, the app is running at 60Hz.