set monitor for clients that don't have one in updatemons()

only if selmon is enabled and the clients are mapped

client.h

@@ -183,6 +183,16 @@ client_is_float_type(Client *c)
 		|| c->surface.xdg->toplevel->parent;
 }
 
+static inline int
+client_is_mapped(Client *c)
+{
+#ifdef XWAYLAND
+	if (client_is_x11(c))
+		return c->surface.xwayland->mapped;
+#endif
+	return c->surface.xdg->mapped;
+}
+
 static inline int
 client_wants_fullscreen(Client *c)
 {

dwl.c

@@ -2365,6 +2365,7 @@ updatemons(struct wl_listener *listener, void *data)
 	 */
 	struct wlr_output_configuration_v1 *config =
 		wlr_output_configuration_v1_create();
+	Client *c;
 	Monitor *m;
 	sgeom = *wlr_output_layout_get_box(output_layout, NULL);
 	wl_list_for_each(m, &mons, link) {
@@ -2388,6 +2389,11 @@ updatemons(struct wl_listener *listener, void *data)
 		config_head->state.y = m->m.y;
 	}
 
+	if (selmon && selmon->wlr_output->enabled)
+		wl_list_for_each(c, &clients, link)
+			if (!c->mon && client_is_mapped(c))
+				setmon(c, selmon, c->tags);
+
 	wlr_output_manager_v1_set_configuration(output_mgr, config);
 }