There's a book for new players in the Agranor library. It states that before upgrading to a newer version, you should create a save file from the moment Celica wakes up in the morning. Otherwise, there may be problems with the automatic save import.
As a last resort, there's an automatic save created at the beginning of each game day; information about this is also available in the library.
When upgrading from one version to another (Linux, Windows, and sometimes Android), there's no need to copy your saves manually. This is because Ren'Py creates a hidden folder for your saves, and the new copy of the game will see it when it launches.