The prior post you mentioned is located
here (for people's convenience). This might be a silly question on my part, but do you have access to a newer update-supported iOS version to try it on by any chance? Even just a newer phone for testing would be fine. I notice you mentioned your iOS software is out of date due to the hardware version (iPad 5, released in 2017) so if you do have access to a more updated one, it would be great to
access your save game files and copy it over to another fully-updated device to check it out on. This might be able to inform the question you mentioned in that other post, of whether or not the issue is related the outdated operating system.
The other thing you could do is post your save files here and someone can test them. Another question is, did you ever do any save file editing that might have gone a bit haywire?
It is absolutely possible to move your save files/game over to a new iOS device, and redownload the prior-purchased Stardew app from the App Store, as long as you're logged into the same iTunes account on the new device. Your save files can easily be copied to iCloud Drive, from the local files app in the old device. Sorry I can't be of better help than this.