Don't use arguments with It and -enum, pointed out by jmc.

tmux.1

@@ -4461,17 +4461,17 @@ as a list of menu items separated by
 .Ql | .
 Each menu item consists of three comma-separated parts:
 .Bl -enum -width Ds
-.It name
+.It
 The menu item name.
 This is a format and may include embedded styles, see the
 .Sx FORMATS
 and
 .Sx STYLES
 sections.
-.It key
+.It
 The menu item shortcut key.
 If this is empty the menu item has no key shortcut.
-.It command
+.It
 The command run when the menu item is chosen.
 .El
 .Pp