This is a meta-analysis of studies published before July 1st, 2020, this means the data covers even less time. This analysis is not irrelevant, but it examines a very small period of time. The 0.2 percent decrease in mortality is the precision weighted average. The full quote is

the studies find that lockdowns, on average, have reduced COVID-19 mortality rates by 0.2% (precision-weighted). The results yield a median of -2.4% and an arithmetic average of -7.3%. Only one of the seven studies, Fuller et al. (2021), finds a significant and (relative to the effect predicted in studies like Ferguson et al. (2020)) substantial effect of lockdowns (-35%).

The precision-weighted average is important, but can't be examined in a vacuum.

All the study concludes is that lockdowns were not an effective way to reduce Covid-19 mortality "during the first wave of the COVID-19 pandemic."

One thing the study is not completely clear about is how they know what would have happened without lockdowns. The authors describe models and the "level of stringency," but there is no way to really know what would have happened if lockdowns did not occur. Healthcare resources (people and material) were extremely limited, would any increase in Covid-19 mortality have lead to even more limited resources that would have lead to a higher mortality rate? Would that shortage of resources have lead to more excess deaths since there were fewer medical resources for other needs?

Lockdowns meant fewer car crashes and job site accidents which could reduce hospitalizations and keep resources focused on Covid patients. People with heart attacks, strokes, and other emergencies would still need treatment, but it's still less than an average day without a lockdown and with a pandemic.

The authors recognize that there may be some cause and effect issues at work, but they downplay it

First, people respond to dangers outside their door. When a pandemic rages, people believe in social distancing regardless of what the government mandates. So, we believe that Allen (2021) is right, when he concludes, “The ineffectiveness [of lockdowns] stemmed from individual changes in behavior: either non-compliance or behavior that mimicked lockdowns.” In economic terms, you can say that the demand for costly disease prevention efforts like social distancing and increased focus on hygiene is high when infection rates are high.

The lockdowns may have convinced some people that Covid is serious and resulted in people taking social distancing seriously. These are people who are not anti-mask, anti-lockdown, anti-vax, but who would have mostly ignored Covid and gone on with their lives if not for the mandates. The mandates also meant that many workplaces shifted to remote, and companies would probably not have done that willingly if there were not mandates. The lockdowns probably contributed to changes in behavior that would not have happened if the lockdowns did not occur. We can never know to what extent this affected the mortality rate.

This study is interesting, but very limited because of the short timeframe studied and because we can never really know what would have happened without lockdowns.