I mostly agree with that, including that supplements are not always needed but I still take them.
For healthy people, there isn't much good evidence that supplements are very useful. They don't seem to improve overall health, lifespan, or cancer risk (except vitamin A might increase risks). Measuring and replacing vitamin D can be beneficial, but even that research is mixed. Some studies show benefits, others don't.
Some supplements can help with specific medical issues. Most research on supplements is low quality, based on smaller studies with mixed results. Many clinical trials lack randomization, placebo controls, or double-blinding. Supplements are not patentable, so there's no huge funding for trials like drug companies have, except for public health issues like vitamin D and fish oil. This means smaller trials that don't prove effectiveness.
This doesn't mean they don't work, but it doesn't mean they do either. You might find positive trials that are low quality. It's below the level needed for guidelines or most doctors to recommend them.
Sometimes you find something with positive trials over years, that aren't contradicted by other studies. And the science behind it makes sense. These are the best bets, but still usually low to moderate quality evidence. It could just be chance that all those results were positive. If you test enough things, some results will be positive several times in a row just by chance or placebo.
I won't list ones with good evidence, it would be too long. If you ask an AI about supplements (or peptides), ask for evidence and how certain that evidence is, by medical standards. You might get a better answer. Most supplement info online outside of journals is untrustworthy because there's too much money to be made by claiming they work.