How to Make Multi User Objects Single User? I duplicated a few objects with Alt+D and now I want to apply some modifiers to them, however I can't, because they are multi-user objects.

I tried U > Objects but I still can't apply the modifier.

How to make multi user objects single user?
Press U > Objects and Data. Then apply your modifier. Using just Object will make the object a new, separate datablock for the mesh (but will ignore modifiers). However, using Object and Data will make both the objects mesh and it's modifiers a new, separate datablock.