We had an on-prem exchange server with some email enabled public folders. Recently we migrated this on-prem server to O365. After the migration we couldn't add any more users to the public folders. Though we have gave them permission from exchange online to those public folder but still the users were not able to find the public folders in their outlook.
Even we tried creating new user from )365 online and granted permission to public folder, still the newly created user didn't find any public folder in his outlook desktop or outlook online.