This Yale study[1] collected data from every county in the US about which restrictions were in place and then tracked how many people got sick. Their data[2] distinguishes between “mask mandate” and a “mask recommendation” and the study author is quoted that the recommendation “doesn’t do anything”. Of course this is all US data so I’m not sure whether or to what extent it would apply to Sweden’s compliance with a mask recommendation vs mandate.
[1]https://insights.som.yale.edu/insights/study-shows-which-res...