1) Not clear how lit review published in 2021 casts doubt on a study published in 2024
2) The lit review does not say the data is controversial, only that the claim of life extension is, and then goes on to say "However, via its ability to reduce early mortality associated with various diseases, including diabetes, cardiovascular disease, cognitive decline and cancer, metformin can improve healthspan thereby extending the period of life spent in good health" which is entirely consistent with the monkey study under discussion here
That article discusses the earlier experiments on nematodes and mice and doubts the applicability to humans of some results.
This new study provides data about positive results in primates, so it removes some of the earlier objections.
Nevertheless, it is not clear yet whether the risks of harmful effects of long-term treatment with high doses of metformin do not outweigh its beneficial effects.
Where I agree with the article linked by you is that metformin is not the actual cause of lifespan extension, but it mimics the effects of some other primary cause, perhaps calorie restriction.
Therefore, the studies on the metformin effects should concentrate on establishing which is the mechanism of its action, even if that is much more difficult than just establishing a correlation between metformin intake and ageing. When the mechanism of metformin action will be understood, it is likely that the same effects will be achievable in safer ways.
Data is controversial. It's not "not enough" data or anything like that either.