Again, it depends on the definition. The movie Passengers (not new I know) could technically be an isekai. They have left the familiar, with practically no way to return to venture a new world. Or isekai could mean an alternate universe. It could also require the rules of the universe to be different. If I remember correctly, there was a story about a woman entering a portal to another universe written in 1666. Margaret Cavendish I believe.