you can still go out the border with the /tp command, but if you go like 2,000,000 blocks out you get to what people call the stripelands, and if you go 2,000,000 blocks out in both x and z, you get to what I call the coordlands/coordinate plane lands cause it's just one piller of blocks every other block, and just to move, you need to be flying with an elytra, spamming rockets