running Blender 2.91.2 and am having two different blend files in which modifiers cannot be applied due to them being "disabled" and cannot be applied to Multi-User data. They work just fine, hell I even just created an array modifier and with the untouched, base settings the modifier is disabled. Am a bit PO right now because deadline is tomorrow. Any help is highly appreciated.
Late to the party on this one. (I was asleep when the question was posted!)
In future, there's a quick way to get over this problem.
Go to the Object Data Properties tab (green triangle). In the Mesh data line you'll see a number next to the shield
Hovering the mouse over the number will show the following popup
Click on that number to make it disappear and you'll then be able to apply the modifier.