Eli5: Why can’t we figure out the planet after Neptune in our Solar System but we are able to find out galaxies thousands of light years away from us ?

Question

Recently have been binge-ing on planets and cosmos, and I saw this youtuber mentioned that we might discover the next planet after Neptune.

However from my understanding, humanity has discovered black holes, magnetars, stars and so on that are hundreds, thousands or even more than that in terms of the measurement of light years.

Our solar system is not in the measurement of light years, yet we can’t discover the next planet after Neptune. Why ?

In: Technology

Answer 1

You go out to the edge of the solar system with a sun-sized flashlight and you’ll find that planet real quick.