Apply GRID_LOOP

Marlin/src/feature/bedlevel/ubl/ubl.cpp

   void unified_bed_leveling::report_current_mesh() {
     if (!leveling_is_valid()) return;
     SERIAL_ECHO_MSG("  G29 I99");
-    LOOP_L_N(x, GRID_MAX_POINTS_X)
-      for (uint8_t y = 0;  y < GRID_MAX_POINTS_Y; y++)
-        if (!isnan(z_values[x][y])) {
-          SERIAL_ECHO_START();
-          SERIAL_ECHOPAIR("  M421 I", int(x), " J", int(y));
-          SERIAL_ECHOLNPAIR_F_P(SP_Z_STR, z_values[x][y], 4);
-          serial_delay(75); // Prevent Printrun from exploding
-        }
+    GRID_LOOP(x, y)
+      if (!isnan(z_values[x][y])) {
+        SERIAL_ECHO_START();
+        SERIAL_ECHOPAIR("  M421 I", int(x), " J", int(y));
+        SERIAL_ECHOLNPAIR_F_P(SP_Z_STR, z_values[x][y], 4);
+        serial_delay(75); // Prevent Printrun from exploding
+      }
   }
 
   void unified_bed_leveling::report_state() {

Marlin/src/gcode/bedlevel/M420.cpp

 
             // Get the sum and average of all mesh values
             float mesh_sum = 0;
-            for (uint8_t x = GRID_MAX_POINTS_X; x--;)
-              for (uint8_t y = GRID_MAX_POINTS_Y; y--;)
-                mesh_sum += Z_VALUES(x, y);
+            GRID_LOOP(x, y) mesh_sum += Z_VALUES(x, y);
             const float zmean = mesh_sum / float(GRID_MAX_POINTS);
 
           #else
 
             // Find the low and high mesh values
             float lo_val = 100, hi_val = -100;
-            for (uint8_t x = GRID_MAX_POINTS_X; x--;)
-              for (uint8_t y = GRID_MAX_POINTS_Y; y--;) {
-                const float z = Z_VALUES(x, y);
-                NOMORE(lo_val, z);
-                NOLESS(hi_val, z);
-              }
+            GRID_LOOP(x, y) {
+              const float z = Z_VALUES(x, y);
+              NOMORE(lo_val, z);
+              NOLESS(hi_val, z);
+            }
             // Take the mean of the lowest and highest
             const float zmean = (lo_val + hi_val) / 2.0 + cval;
 
           if (!NEAR_ZERO(zmean)) {
             set_bed_leveling_enabled(false);
             // Subtract the mean from all values
-            for (uint8_t x = GRID_MAX_POINTS_X; x--;)
-              for (uint8_t y = GRID_MAX_POINTS_Y; y--;) {
-                Z_VALUES(x, y) -= zmean;
-                #if ENABLED(EXTENSIBLE_UI)
-                  ExtUI::onMeshUpdate(x, y, Z_VALUES(x, y));
-                #endif
-              }
+            GRID_LOOP(x, y) {
+              Z_VALUES(x, y) -= zmean;
+              #if ENABLED(EXTENSIBLE_UI)
+                ExtUI::onMeshUpdate(x, y, Z_VALUES(x, y));
+              #endif
+            }
             #if ENABLED(ABL_BILINEAR_SUBDIVISION)
               bed_level_virt_interpolate();
             #endif