If I were to start again, I would look outside of my tech bubble. Go see a local workshop, baker, restaurant. Look into niche industries. There are plenty of inefficiencies and unsolved problems there. I think the best ones are where you deal with physical things (e.g. not just advertising or getting customers).

There are plenty of unsolved problems.

An alternative is to look for a problem that has been "solved", but not in a certain niche. For example, inventory control and tracking production seems to be a "solved" problem, but it turned out it wasn't a "solved" problem for small/medium-scale electronics manufacturing, which is the niche I'm in.