Well... you sound youngish so let's not write off the possibility that there's time for both. But here's some thoughts and some experience
a) What thing doesn't exist and you've noticed it hasn't existed for ages? A lack of the thing being both apparent and long-term is how you can assume that nobody else is going to do it.
b) What thing that nobody else is going to do can you do? Me, I definitely can't invent a new kind of battery, but I can apply my ADHD and ASD quirks to a certain kind of civic tech problem that involves pushing a gigantic and annoying rock of data up a hill _once_, then spending hardly any time per project keeping it ticking over.
c) What thing that doesn't exist and which you can do needs doing? My field is regularly jostled around by some kid or other whose "startup" barges in, makes a pile of noise, never makes a dime, stinks up the water some, then vanishes without trace. I get the feeling that jumping into things without adequate consideration for the potential harm is likely not your largest problem [ :) ] but other people will be reading this page.
The first civic tech thing I did (kildarestreet.com) is a searchable transcript of everything that happens in the Irish parliament. It didn't exist when I moved here 14 years ago, it really did need to because the official version of the same data was -- some would say purposefully -- utterly unusable, and I'd just moved over from the UK where the original version of the same app (theyworkforyou.com) was A Thing That People Use A Lot. I was able to put it together -- perhaps would not have if I'd known I'd be rewriting all the parsers for a third time ten years later -- with my skill set, and critically, very obviously nobody else was going to get it done. There's all my tickboxes for whether this is worth spending time on.
d) I should add here that "is it practically possible to do" factors here because I got into this whole thing trying to build something else entirely. Ireland did not have a way for me as a new resident to find out which electoral district I lived in, and thus who represented me at local and national level. In the UK writetothem.com from the same people as made the other stuff tells you this when you enter a postcode on the homepage and simply choose not to write someone a letter. That's what I tried to do first, in an itch-scratching manner. But it stalled because there was in 2006 no way to convert an address to a geo point without spending €72000/yr so eventually, irritated by that, I moved down the list to the lowest-hanging fruit instead. So also, don't spend forever trying to do the undoable.
You'll notice none of this mentions how in the fuck you pay your rent. I do other things and take donations. Some people start companies. Some are grant-aided. Some are just rich to start with. But this isn't strictly what you asked :D