I believe that is what pre-COVID masking in hospital settings has shown, yes. Possibly COVID is different from the flu.

But the difficulty for proving masking helps is: 1. If it only takes ~20 virions to get infected, then masking has to have a basically perfect filtering rate and be worn perfectly 100% of the time, neither of which is obvious. 2. With an endemic virus even if masks slow down spread they aren't going to reduce your likelihood of being infected overall.