I disagree with this. There are plenty of counterexamples where an individual can have a measurably positive impact on their own life. Solar + batteries comes to mind.
Also in your linked example, you brought up reading and literacy as something that would not improve collective problems, and I couldn't disagree more.
Feels like you're on a different tack here: improving your "own life" is different from solving "collective problems".
Further, setting up solar + batteries solves a non-modest individual problem, but is not by itself (i.e. reducing carbon footprint; an example mentioned in the parent's link) the solution to climate change. (yes it helps; but incentives leading to people installing solar have a much bigger impact; and the biggest incentive was maybe China building a solar panel industry, but I'm not trying to go down that tangent)
That's fair. I think I had read the parent a little differently. I was interpreting this as situations where an individual can improve their own experience of a collective problem, in a way accessible to most. But I acknowledge that's a bit different.
With the solar+battery, I was thinking of solving grid issues and energy prices, which it does do.
Unfortunately, individual action doesn't have significant effects - the article mentions leaded fuels, that wasn't something that could be done by individuals alone. You mention solar + batteries but to be blunt, that's only something middle class homeowners can afford, and they're a minority. Maybe some landlords in housing projects but they want government funding for that.