bugfix:

- Add init totals into foreach rules loop to allow for total calculation after each rules apply on Discount.php

- remove logic for adding item discount to address base discount on Discount.php

- on CartFixed.php now use validator to calculate current valid items total discount for rule on proporcional discount calculation.

refs: magento#38694

app/code/Magento/SalesRule/Model/Quote/Discount.php

@@ -188,7 +188,6 @@ public function collect(
         $items = $this->calculator->sortItemsByPriority($items, $address);
         $itemsToApplyRules = $items;
         $rules = $this->calculator->getRules($address);
-        $totalDiscount = 0;
         $address->setBaseDiscountAmount(0);
         /** @var Rule $rule */
         foreach ($rules as $rule) {
@@ -221,11 +220,9 @@ public function collect(
                     unset($itemsToApplyRules[$key]);
                 }
 
-                $totalDiscount += $item->getBaseDiscountAmount();
             }
-            $address->setBaseDiscountAmount($totalDiscount);
+            $this->calculator->initTotals($items, $address);
         }
-        $this->calculator->initTotals($items, $address);
         foreach ($items as $item) {
             if (!isset($itemsAggregate[$item->getId()])) {
                 continue;

app/code/Magento/SalesRule/Model/Rule/Action/Discount/CartFixed.php

@@ -81,6 +81,8 @@ public function calculate($rule, $item, $qty)
         $ruleTotals = $this->validator->getRuleItemTotalsInfo($rule->getId());
         $baseRuleTotals = $ruleTotals['base_items_price'] ?? 0.0;
         $ruleItemsCount = $ruleTotals['items_count'] ?? 0;
+        $ruleItemsBaseDiscount = $ruleTotals['base_items_discount_amount'] ?? 0.0;
+
 
         $address = $item->getAddress();
         $quote = $item->getQuote();
@@ -133,7 +135,7 @@ public function calculate($rule, $item, $qty)
                         $qty,
                         $baseItemPrice,
                         $baseItemDiscountAmount,
-                        $baseRuleTotals - $address->getBaseDiscountAmount(),
+                        $baseRuleTotals - $ruleItemsBaseDiscount,
                         $discountType
                     );
             }