I'm using an Office 365 or Exchange account with modern authentification, i need to access the public folders but it seems to be not listed in Automatic Email Manager.
The answer from Microsoft:
Public folders aren't supported in the Graph API and given there legacy status I don't think they will be at any point in the near future so you will need to use EWS with basic Auth for any Public Folder applications. If your building a greenfield application the best advice is don't use Public Folders, look at either SharePoint or Office365 Groups if it's an email based application which offers much more functionally and future support and growth path.
Microsoft recommended us to no more use Basic auth and remove EWS, to use only Microsoft modern api GRAPH with modern auth. I'm sorry for your case as now it is not possible to use public folder, the only way is to use shared email boxes (to share email box between multiple users).