in the picture below u will see there is me the owner and im sharing the folder with everyone on the network. but how do i determine who the unknown user is and can i or should i remove them?
It could be a user that was once on the network but cannot be contacted (Possible password change, user deletion or other user changes). That being said, since you have the folder shared to everyone it would be safe to remove that user since anyone may access the share regardless of their user credentials