It literally says " 'We are uncertain whether wearing masks or N95/P2 respirators helps to slow the spread of respiratory viruses based on the studies we assessed.' "

That means that the study was inconclusive. Even in the most mask-active trial, only ~42% of people wore masks. They weren't testing if wearing a mask helps an individual not get sick, they were measuring if it slowed the spread of a respiratory virus. Of less than half of people wear a mask, it makes it REALLY hard to know if the masks made an impact in reducing the spread of a contagious respiratory virus.

Let's think about this in the context of something not directly covid related - secrets. In a crowd of 500 people, if you tell one person a secret, and then tell them to tell as many people as they can, even if 40% of people in that crowd are wearing earplugs, most people are going to end up hearing that secret. Even some of the people with earplugs in might have them not in all the way, or have taken them out for a moment to adjust them, and heard the secret. But, the people with earplugs will be much less likely to have heard the secret.

That's COVID and masks. Unless EVERYONE is wearing a mask, it makes it really hard to stop spreading of the virus, even if individuals wearing masks are less likely to catch or spread the virus themselves.