Use `org-loop-over-siblings-in-active-region' for `org-archive-set-tag'.

lisp/org-archive.el

@@ -462,7 +462,8 @@ the children that do not contain any open TODO items."
 (defun org-archive-set-tag ()
   "Set the ARCHIVE tag."
   (interactive)
-  (org-toggle-tag org-archive-tag 'on))
+  (org-loop-over-siblings-in-active-region
+   (org-toggle-tag org-archive-tag 'on)))
 
 ;;;###autoload
 (defun org-archive-subtree-default ()

lisp/org.el

@@ -1983,7 +1983,8 @@ The list of commands is:
 - `org-deadline'
 - `org-archive-subtree'
 - `org-archive-to-archive-sibling'
-- `org-archive-set-tag'"
+- `org-archive-set-tag'
+- `org-toggle-archive-tag'"
   :group 'org-todo
   :group 'org-archive)