Scan lines are enabled by default in Animal Well, as it imitates the effects that you see in old-school CRT televisions. If you would rather turn these off, then you can check out this guide at Seeking Tech to see how you can properly do so.
1. To start off, open up the Paused menu.
2. You then need to head into Options.
3. From there, make sure that the Scanlines setting is disabled.
4. Exit the menus and you should no longer see any scanlines when you return to playing Animal Well.