I don't know if it's low-hanging. In my experience finding what you are REALLY interested in involves a lot of trial and error, while aptitude tests are worthless beyond the pretty obvious division into techies and humanities people.

Certainly this seems like a (meta-)low-hanging fruit.

There seem to be fairly effective interest / aptitude tests, that I remember taking in middle school. The level of detail is insufficient to identify low-hanging fruits ("you should go work in this particular research group") but is still narrow enough to be useful ("these are the jobs that the 0.1% of the population most like you finds most satisfying"). This can raise to attention jobs or fields that are high impact or high paying that someone might not be consciously aware of, or realize that it suits them well. (The canonical example here is MRI sales; someone has to sell them, but a person with strong ability to remember facts and figures and understand technical things, and also to deal with people, may not have that come to mind as an intersection of their interests and aptitudes.)

In my view, a lot of the lack of "low hanging fruit" many people see is working in the wrong field. Some fields (for example, computer science) are extremely saturated with very bright people. As Lumifer suggested, sampling different potential interests is a reasonable strategy. I've been surprised by the random things that turned out to be fascinating to me.

Many opportunities exist in fields where certain knowledge is useful but rare. For example, there are many fields where math and coding knowledge could make a big impact. I know someone who got a PhD in math and then started working on problems related to fire protection. The specific application is not so critical, but the rarity of their ability in that field is. They seem to love their job, and I think this is a generally useful strategy. You just need to find fields in the intersection of problems of sufficient interest to you and problems your skills and knowledge can help solve. Some other examples: math and programming knowledge could be super useful in psychology and medicine.

Part of the problem here is a hidden constraint that I see from many people. Many smart people seem to believe many fields are below them, and they won't consider them because of this. You should see the fields that other people are avoiding for this reason as opportunities.

In terms of finding these sorts of opportunities, I don't think there's a good general procedure other than seeing how your current knowledge could fit into any field you encounter, and taking action when you see opportunity.