I often see this flickering in my network monitoring app when I run it on my Pixel 8 phone with Graphene OS. From what I understand, not all phones have this problem with my app, even on other phones running Graphene OS. For my Pixel 8, the flickering seems limited to my own app, and the phone dialer, at least when using Cheogram to make calls:
https://discuss.grapheneos.org/d/8251-jmpchatcheogram-and-audio-output-device-issue
I've seen flicker on my phone when navigating GitHub issues pages, but that's likely due to JS jank.
There are a number of recent GitHub issues that mention issues with flickering on the Flutter issues tracker, so I wonder if this is the problem. Here's one issue that I've commented on:
https://github.com/flutter/flutter/issues/160824
I'll try applying your advice to see if that helps.