The undo should name the thing
A reversible action is easier to trust when the interface says what will be reversed.
I am suspicious of an Undo button that refuses to say what it will undo.
The interface archives a file, removes a tag, or moves a note. A small toast appears: "Undo." It gives me a few seconds to reverse the change, but not enough information to know whether I am bringing back the file, restoring the tag, or moving the note again. If I miss the timer, the evidence disappears with it.
The label can be plain: "Undo archive" or "Restore September notes." Keep the target beside it: "Archived: September notes." If several actions can be reversed, give me a small history instead of making each change disappear with the toast.
The timer can stay. I understand why an interface uses one. I just want the system to leave a sentence behind when it changes something. Reversing an action is easier when I can tell exactly what I am reversing.