Mini Motorways only supports one save file, though if you are playing on Apple Arcade and have multiple Apple devices you may be able to resume the Endless game on a separate device before starting a new game on the original device. For example, if you leave your Endless game on your iPhone, and then resume the same game on your Mac before starting a new game on your iPhone, you will be able to save the original Endless game on your Mac. Otherwise, you can preserve your city forever using the photo mode or GIF creation tools located in the lower right corner of the pause menu before leaving your Endless game.