Here's the cheat code for you: look at what businesses are constantly spending money on, and you will find plenty of business ideas. There will be competition, most likely a lot of it, but don't let that deter you. Competition means there's money to be made in the market, and people are already aware of the problem so that you don't have to educate them on why they need a solution (you will have to clearly communicate why your product is better, though).
When going after existing markets, you basically swap an idea validation challenge with a sales and marketing challenge. Before launching my business, I had a misconception that if you're already solving a problem, you don't have to do much marketing and sales - WRONG! You still have to get in front of existing customers, repeatedly.
Going after an existing market doesn't mean you have to launch a carbon copy of an existing product. You can differentiate by a price (probably not a good idea), by a combination of features, or by having a polished UI/UX/Developer experience. If your competitors suck, you can differentiate by virtue of not being broken (e.g. "Product X just works" can be your shtick). You can also out-market your competition (here's the one thing they don't want you to know: better products don't usually win over better-marketed products).
Why businesses you might ask? Because they're not reluctant to part with their money if you can either save or make them money. You will have a higher average revenue per user (ARPU), which means you can spend more money on acquiring customers (CAC is the term-of-art) than if you were in B2C. You will also need fewer customers to reach your revenue goals, which will translate into less support.
If your goal is to build a sustainable business, I think this is the most optimal approach to take. Just make sure you're not in the winner-takes-all type of market.