Mirror Modifier's Apply button is grayed out even in Object Mode


I am not sure what I am doing wrong but I can’t apply my mirror modifiers because when I go to Object Mode and try to apply the modifier, the Apply option is grayed out:

I am not sure what I am doing wrong…?

It’s a linked duplicate (i.e. you have more than one object using the same mesh). Blender doesn’t allow to apply modifiers to linked duplicates.
To fix it manually you’ll need to make the object single-user, apply the modifier, then re-link to other objects. Or you can use the Modifier List add-on which can do that for you at the press of a button.

Thank you very much! sounds like this is it!