Fixed Importing: non-default multiple value separator can't be used in custom multiple select attribute

app/code/Magento/CatalogImportExport/Model/Import/Product.php

@@ -46,6 +46,7 @@
  */
 class Product extends AbstractEntity
 {
+    private const DEFAULT_GLOBAL_MULTIPLE_VALUE_SEPARATOR = ',';
     public const CONFIG_KEY_PRODUCT_TYPES = 'global/importexport/import_product_types';
     private const HASH_ALGORITHM = 'sha256';
 
@@ -2841,6 +2842,10 @@ private function parseAttributesWithWrappedValues($attributesData)
     public function parseMultiselectValues($values, $delimiter = self::PSEUDO_MULTI_LINE_SEPARATOR)
     {
         if (empty($this->_parameters[Import::FIELDS_ENCLOSURE])) {
+            if ($this->getMultipleValueSeparator() !== self::DEFAULT_GLOBAL_MULTIPLE_VALUE_SEPARATOR) {
+                $delimiter = $this->getMultipleValueSeparator();
+            }
+
             return explode($delimiter, $values);
         }
         if (preg_match_all('~"((?:[^"]|"")*)"~', $values, $matches)) {

dev/tests/integration/testsuite/Magento/CatalogImportExport/Model/Import/ProductTest/ProductValidationTest.php

@@ -373,4 +373,32 @@ public function testProductWithInvalidWeight()
             $errors->getErrorByRowNumber(1)[0]->getErrorMessage()
         );
     }
+
+    /**
+     * Test validate multiselect values with custom separator
+     *
+     * @magentoDataFixture Magento/Catalog/_files/products_with_multiselect_attribute.php
+     * @magentoAppIsolation enabled
+     * @magentoDbIsolation enabled
+     *
+     * @return void
+     */
+    public function testValidateMultiselectValuesWithCustomSeparator(): void
+    {
+        $pathToFile = __DIR__ . './../_files/products_with_custom_multiselect_values_separator.csv';
+        $filesystem = $this->objectManager->create(Filesystem::class);
+        $directory = $filesystem->getDirectoryWrite(DirectoryList::ROOT);
+        $source = $this->objectManager->create(Csv::class, ['file' => $pathToFile, 'directory' => $directory]);
+        $params = [
+            'behavior' => Import::BEHAVIOR_ADD_UPDATE,
+            'entity' => 'catalog_product',
+            Import::FIELD_FIELD_MULTIPLE_VALUE_SEPARATOR => '|||'
+        ];
+
+        $errors = $this->_model->setParameters($params)
+            ->setSource($source)
+            ->validateData();
+
+        $this->assertEmpty($errors->getAllErrors());
+    }
 }

dev/tests/integration/testsuite/Magento/CatalogImportExport/Model/Import/_files/products_with_custom_multiselect_values_separator.csv

@@ -0,0 +1,2 @@
+sku,store_view_code,product_type,name,price,additional_attributes
+simple_ms_2,,simple,"With Multiselect 2",10,"multiselect_attribute=Option 2|||Option 3"