After the great migration, when it became clear that new people who arrived from a parallel world did not pose a threat to humanity, all kinds of objects with technologies from another world were installed all over the planet, helping people and making life more comfortable.

When, after 23 years of successful living together, "new people" suddenly disappeared in one moment, humanity panicked. But nothing happened. Over time, people calmed down, and just forgot about the incomers.
Alien objects eventually completely or partially failed. And since people did not really know the principles of their work, then the broken object was simply transported away from their places of residence and left them there.

Now, walking in deserted abandoned places, you can often find these destroyed, and sometimes even working objects.