I think they mean a side-gig or business, a SaaS essentially. While I disagree with them that they 'are a waste of time', it depends entirely on the 'what'.
A lot of bars have shifted in a never-been-seen-before way. Many intractable or unsolvable problems for a single developer, that required teams and 6 months or years, can now be solved in a few evenings.
That does NOT mean that everyone is capable of doing this. Which leads to my argument that there is still a market for many ideas, just not your kanban boards, todo lists or scheduling assistants. Have to look beyond at harder problems (the author mentions a few good ones) that solve a genuine user need end-to-end. This also means niche products are low-effort now and could be worth doing, even for a few select customers.
My favorite kind are developing new software for niche/old devices, to make them do new things. People who are making old TVs usable again for lack of software support are my heroes.