I think there is a problem with trying to target your attention on world changing technology, in that it is very rare for the world to be changed in a big way by direct effort towards change. I think this is related to both the difficulty in identifying what will really provide benefit and also the difficulty in actually achieving anything beyond incremental change to mature technology. Ideas that really make a difference tend to come out of left field and are almost completely unexpected.
If you are looking for something to do that you will look back from your death bed and say "I did that", then you need to select something that you can actually achieve. This will not be the thing that everybody else is working on, because unless you are truely remarkable your effort will be lost in the noise of what everybody else is doing. You need to find something that your both enjoy, and after honest evaluation you have the ability to excel in and take to the next level.
If you were living in the early 1900's I would suggest working on the field effect produced when electricity is passed through centain types of silicon. No one will know your name, but transistors certainly changed the world. How in 2019 do you identify what will have a similar impact? Simply put, you can't. All you can do is pick something interesting and work at it. If you try to solve the big problem you will almost certainly get drowned in the problem, you need to work on something small that can be leveraged to make the big thing.
Sorry I ramble.
History is full of people who made big changes to the world. Those who made a positive contribution seem to mostly have emerged from obsecurity after spending years labouring at improving something small and succeeding in a remarkable way.