This is not meant as a guide to make money or other economic advice, but if I was looking for profitable businesses or sectors, I'd -among other things- look at their relative position in the chain of added value.

One example that shows the opposite of profitability, a business model that was good enough to survive but not good enough to pay more than bills:

I once calculated a business plan for a company that was modelled after another company. The other, existing, company had agreed to provide me internal data. Their reasoning was that the market needed more marketeers to widen demand and needed more companies in business to assure customers of security of supply. an additional competitor was more of a gift than a problem in this sector.
So I calculated and calculated and the result was no substantial profit under realistic assumptions. That turned out to be correct for the existing company.
Here's why:
The companies of that sector processed a single raw material. Their suppliers (farmers) were able to choose freely whether they want to supply this raw material or instead grow something else. The customers for the processed stuff on the other hand were free to choose freely between it and multiple synthetic substitutes.
These processing businesses were in a sandwich; zero market power against suppliers and zero market power against customers. Their only hope of profit laid in their skill at misleading their business partners about how much was left to squeeze out of themselves.

The opposite - a company with superior relative market power against suppliers AND customers - is almost inevitably a gold mine.