First off, you need to create a small list of topics, interests, or skills that you are good at (or have expertise in) and enjoy. This is the ideal combination, and in general, people enjoy things that they are good at.
When building an online business you want it to be based around something that you are passionate about otherwise you risk getting burnt out and losing interest.
Try not to write down topics that you don’t particularly enjoy even if you have years of experience in on that topic. For me, I had over 6 years of experience in insurance, but there was no way I was going to create a website about insurance because it didn’t excite me and I was sick of it.
If you’re having trouble coming up with something that fits all of this criteria just write down a couple topics that you’re interested in and would really enjoy learning more about and becoming an expert in.
Here are a few examples of topics: a certain sport, fitness, nutrition, finance, video games, photography, ect.
Take a couple minutes right now and create a list of 2-3 topics, don’t write down too many topics, you’ll only overwhelm yourself if your list becomes too big.