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build something original or financially viable> I‘ve had dozens of ideas I didn’t pursue further after asking myself „if this is such a great idea, why hasn’t somebody else already done it?“.
You're conflating the two ("original" and "financially viable"). In my opinion, your mindset is fundamentally flawed. I'm not saying this in a negative way, I just mean that I've seen it before in others, and I myself used to think like you, so I can understand what you mean.
The truth is, clones make money. You don't need an original idea to be financially successful, at the 4 to 8 figure range. Indeed, if you simply want to quit your job rather than make billions, you should be in a market with many competitors so you can carve out a small slice of it. If you instead are building a whole new market, like Airbnb or Uber, you can carve out a much larger slice but that requires a fundamentally different way of working, ie raising lots of money, teaching your audience (before Uber, who'd get in an unlicensed stranger's car?), and marketing the hell out of your startup.
Instead, find a nice, large market with lots of competitors, and start building something. As you build, you will naturally find competitive advantages that differentiate you from your competitors. I also thought I needed to find something totally unique and original, ie an all new market, but I realized that was not the way to have success. Instead, I use an already successful market but then build something in those spaces.
See https://indiehackers.com for more info.