This is why I said “most containers most of the time should”. It’s a bad practice to write to the inside of the container and a better practice to treat them as immutable. You can go as far as actively preventing them from writing to themselves when you build them or in certain container runtimes, but this is not usually how they work by default.

Also a container that is stopped and restarted will not lose its internal changes in most runtimes. The container needs to be deleted and recreated from the image to do that