Ah the thing about automating App Store screenshots with Fastlane is that it also becomes a visual automated test where you find bugs at the last minute (bad dark mode icon here)
@paulgessinger For devices, I have to update the devices list manually in the Snapfile with whatever simulator names the latest Xcode has. After that, most of my unreliability comes from XCUITests per-se, not from issues related to Fastlane (e.g. system-level accessibility IDs changing)
For frames/text, I use Picasso. It works for what i need it to do: i like that it understands Fastlane's snapshot structure. It is crashy and sometimes fiddly about updating screenshots though (i always have to delete its prior screenshots before syncing it with fastlane, or it won't sync fully). There may be better tools out there these days.