perhaps even this is tl;dr, but i'd recommend the whole article if you'd like a better understanding of the benefits and limitations of wearing masks to help prevent the transmission of airborne viruses ; please note this is not limited to covid-19
"Our results have important implications for understanding and communicating preventive measures against the transmission of airborne viruses including SARS-CoV-2. When people see images or videos of millions of respiratory particles exhaled by talking or coughing, they may be afraid that simple masks with limited filtration efficiency (e.g., 30-70%) cannot really protect them from inhaling these particles. However, as only few respiratory particles contain viruses and most environments are in a virus-limited regime, wearing masks can indeed keep the number of inhaled viruses in a low Pinf regime and explain the observed efficacy of face masks in preventing the spread of COVID-19. However, unfavorable conditions and the large variability of viral loads may lead to a virus-rich regime in certain indoor environments, such as medical centers treating COVID-19 patients. In such environments, high efficiency masks and further protective measures like efficient ventilation should be used to keep the infection risk low. The nonlinear dependence of mask efficacy on airborne virus concentration, i.e., the higher mask efficacy at lower virus abundance, also highlights the importance of combining masks with other preventive measures. Effective ventilation and social distancing will reduce ambient virus concentrations and increase the effectiveness of face masks in containing the virus transmission. Moreover, high compliance and correct use of masks is important to ensure the effectiveness of universal masking in reducing the reproduction number (supplementary text, section S7.3, and fig. S11) (20)."