I've glanced through the thread but curious:
What specifically isn't working under Mail in iPadOS and iOS? I did experience issues with syncing and fetching on my Mac Pro's between my iPhone 11 Pro and iPad Pro 11" but they seemed to be resolved under iOS 13.3.1 and weren't as prominent as more updates were released. Specifically, Anytime I checked my Mail on any of my devices, it wouldn't immediately reflect on my other devices. Initially, at some point after iOS 13 was released (as a developer this wasn't a bug I experienced but some did, not many as I recall), I experienced such a lag that I had to close down the app and even restart my devices to get syncing to properly function. Now, there is a slight lag (20-30 seconds at most) before the mail app on my iDevices reflects any changes made.
Otherwise, I find the Mail app in iOS 13 to finally be decent enough for an everyday driver. Improved flags is especially welcome although I wish flag syncing between macOS and iPadOS/iOS would be added instead of just color options.
What specifically isn't working under Mail in iPadOS and iOS? I did experience issues with syncing and fetching on my Mac Pro's between my iPhone 11 Pro and iPad Pro 11" but they seemed to be resolved under iOS 13.3.1 and weren't as prominent as more updates were released. Specifically, Anytime I checked my Mail on any of my devices, it wouldn't immediately reflect on my other devices. Initially, at some point after iOS 13 was released (as a developer this wasn't a bug I experienced but some did, not many as I recall), I experienced such a lag that I had to close down the app and even restart my devices to get syncing to properly function. Now, there is a slight lag (20-30 seconds at most) before the mail app on my iDevices reflects any changes made.
Otherwise, I find the Mail app in iOS 13 to finally be decent enough for an everyday driver. Improved flags is especially welcome although I wish flag syncing between macOS and iPadOS/iOS would be added instead of just color options.