diff --git a/UPGRADE-7.4.md b/UPGRADE-7.4.md
index 487bf6f5007a6..e6de8bedc4918 100644
--- a/UPGRADE-7.4.md
+++ b/UPGRADE-7.4.md
@@ -22,3 +22,8 @@ HttpClient
 ----------
 
  * Deprecate using amphp/http-client < 5
+
+Serializer
+----------
+
+ * Deprecate datetime constructor as a fallback, in version 8.0 a `Symfony\Component\Serializer\Exception\NotNormalizableValueException` will be thrown when a date could not be parsed using the default format.
diff --git a/src/Symfony/Component/Serializer/CHANGELOG.md b/src/Symfony/Component/Serializer/CHANGELOG.md
index 1b5c95cd39443..2e800a62af044 100644
--- a/src/Symfony/Component/Serializer/CHANGELOG.md
+++ b/src/Symfony/Component/Serializer/CHANGELOG.md
@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+7.4
+---
+
+ * Deprecate datetime constructor as a fallback, in version 8.0 a `Symfony\Component\Serializer\Exception\NotNormalizableValueException` will be thrown when a date could not be parsed using the default format
+
 7.3
 ---
 
diff --git a/src/Symfony/Component/Serializer/Normalizer/DateTimeNormalizer.php b/src/Symfony/Component/Serializer/Normalizer/DateTimeNormalizer.php
index a136ec227a3ae..e520063531f13 100644
--- a/src/Symfony/Component/Serializer/Normalizer/DateTimeNormalizer.php
+++ b/src/Symfony/Component/Serializer/Normalizer/DateTimeNormalizer.php
@@ -128,7 +128,11 @@ public function denormalize(mixed $data, string $type, ?string $format = null, a
                 }
             }
 
-            return new $type($data, $timezone);
+            $dateTimeObject = new $type($data, $timezone);
+
+            trigger_deprecation('symfony/serializer', '7.4', \sprintf('A "%s" will be thrown when a date could not be parsed using the default format "%s".', NotNormalizableValueException::class, $defaultDateTimeFormat));
+
+            return $dateTimeObject;
         } catch (NotNormalizableValueException $e) {
             throw $e;
         } catch (\Exception $e) {
diff --git a/src/Symfony/Component/Serializer/Tests/Normalizer/DateTimeNormalizerTest.php b/src/Symfony/Component/Serializer/Tests/Normalizer/DateTimeNormalizerTest.php
index 81219652b3ef1..dfe80452522ec 100644
--- a/src/Symfony/Component/Serializer/Tests/Normalizer/DateTimeNormalizerTest.php
+++ b/src/Symfony/Component/Serializer/Tests/Normalizer/DateTimeNormalizerTest.php
@@ -12,6 +12,7 @@
 namespace Symfony\Component\Serializer\Tests\Normalizer;
 
 use PHPUnit\Framework\TestCase;
+use Symfony\Bridge\PhpUnit\ExpectDeprecationTrait;
 use Symfony\Component\Serializer\Exception\InvalidArgumentException;
 use Symfony\Component\Serializer\Exception\UnexpectedValueException;
 use Symfony\Component\Serializer\Normalizer\DateTimeNormalizer;
@@ -21,6 +22,8 @@
  */
 class DateTimeNormalizerTest extends TestCase
 {
+    use ExpectDeprecationTrait;
+
     private DateTimeNormalizer $normalizer;
 
     protected function setUp(): void
@@ -242,15 +245,25 @@ public function testDenormalize()
         $this->assertEquals(new \DateTimeImmutable('2016/01/01', new \DateTimeZone('UTC')), $this->normalizer->denormalize('2016-01-01T00:00:00+00:00', \DateTimeInterface::class));
         $this->assertEquals(new \DateTimeImmutable('2016/01/01', new \DateTimeZone('UTC')), $this->normalizer->denormalize('2016-01-01T00:00:00+00:00', \DateTimeImmutable::class));
         $this->assertEquals(new \DateTime('2016/01/01', new \DateTimeZone('UTC')), $this->normalizer->denormalize('2016-01-01T00:00:00+00:00', \DateTime::class));
-        $this->assertEquals(new \DateTime('2016/01/01', new \DateTimeZone('UTC')), $this->normalizer->denormalize('  2016-01-01T00:00:00+00:00  ', \DateTime::class));
         $this->assertEquals(new DateTimeImmutableChild('2016/01/01', new \DateTimeZone('UTC')), $this->normalizer->denormalize('2016-01-01T00:00:00+00:00', DateTimeImmutableChild::class));
         $this->assertEquals(new DateTimeImmutableChild('2016/01/01', new \DateTimeZone('UTC')), $this->normalizer->denormalize('2016-01-01T00:00:00+00:00', DateTimeImmutableChild::class));
         $this->assertEquals(new DateTimeChild('2016/01/01', new \DateTimeZone('UTC')), $this->normalizer->denormalize('2016-01-01T00:00:00+00:00', DateTimeChild::class));
-        $this->assertEquals(new DateTimeChild('2016/01/01', new \DateTimeZone('UTC')), $this->normalizer->denormalize('  2016-01-01T00:00:00+00:00  ', DateTimeChild::class));
         $this->assertEquals(new \DateTimeImmutable('2023-05-06T17:35:34.000000+0000', new \DateTimeZone('UTC')), $this->normalizer->denormalize(1683394534, \DateTimeImmutable::class, null, [DateTimeNormalizer::FORMAT_KEY => 'U']));
         $this->assertEquals(new \DateTimeImmutable('2023-05-06T17:35:34.123400+0000', new \DateTimeZone('UTC')), $this->normalizer->denormalize(1683394534.1234, \DateTimeImmutable::class, null, [DateTimeNormalizer::FORMAT_KEY => 'U.u']));
     }
 
+    /**
+     * @group legacy
+     */
+    public function testDenormalizeAndShowDeprecation()
+    {
+        $this->expectDeprecation('Since symfony/serializer 7.4: A "Symfony\Component\Serializer\Exception\NotNormalizableValueException" will be thrown when a date could not be parsed using the default format "Y-m-d\TH:i:sP".');
+        $this->assertEquals(new \DateTime('2016/01/01', new \DateTimeZone('UTC')), $this->normalizer->denormalize('  2016-01-01T00:00:00+00:00  ', \DateTime::class));
+
+        $this->expectDeprecation('Since symfony/serializer 7.4: A "Symfony\Component\Serializer\Exception\NotNormalizableValueException" will be thrown when a date could not be parsed using the default format "Y-m-d\TH:i:sP".');
+        $this->assertEquals(new DateTimeChild('2016/01/01', new \DateTimeZone('UTC')), $this->normalizer->denormalize('  2016-01-01T00:00:00+00:00  ', DateTimeChild::class, null, [DateTimeNormalizer::FORMAT_KEY => null]));
+    }
+
     public function testDenormalizeUsingTimezonePassedInConstructor()
     {
         $timezone = new \DateTimeZone('Japan');
@@ -284,15 +297,11 @@ public function testDenormalizeUsingTimezonePassedInContext($input, $expected, $
 
     public static function denormalizeUsingTimezonePassedInContextProvider()
     {
-        yield 'with timezone' => [
-            '2016/12/01 17:35:00',
-            new \DateTimeImmutable('2016/12/01 17:35:00', new \DateTimeZone('Japan')),
-            new \DateTimeZone('Japan'),
-        ];
         yield 'with timezone as string' => [
             '2016/12/01 17:35:00',
             new \DateTimeImmutable('2016/12/01 17:35:00', new \DateTimeZone('Japan')),
             'Japan',
+            'Y/m/d H:i:s',
         ];
         yield 'with format without timezone information' => [
             '2016.12.01 17:35:00',
@@ -376,10 +385,14 @@ public function testDenormalizeDateTimeStringWithDefaultContextFormat()
         $this->assertSame('01/10/2018', $denormalizedDate->format($format));
     }
 
+    /**
+     * @group legacy
+     */
     public function testDenormalizeDateTimeStringWithDefaultContextAllowsErrorFormat()
     {
         $format = 'd/m/Y'; // the default format
         $string = '2020-01-01'; // the value which is in the wrong format, but is accepted because of `new \DateTimeImmutable` in DateTimeNormalizer::denormalize
+        $this->expectDeprecation('Since symfony/serializer 7.4: A "Symfony\Component\Serializer\Exception\NotNormalizableValueException" will be thrown when a date could not be parsed using the default format "d/m/Y".');
 
         $normalizer = new DateTimeNormalizer([DateTimeNormalizer::FORMAT_KEY => $format]);
         $denormalizedDate = $normalizer->denormalize($string, \DateTimeInterface::class);
diff --git a/src/Symfony/Component/Serializer/Tests/Normalizer/ObjectNormalizerTest.php b/src/Symfony/Component/Serializer/Tests/Normalizer/ObjectNormalizerTest.php
index 439dce056995c..fd59f97831761 100644
--- a/src/Symfony/Component/Serializer/Tests/Normalizer/ObjectNormalizerTest.php
+++ b/src/Symfony/Component/Serializer/Tests/Normalizer/ObjectNormalizerTest.php
@@ -717,7 +717,7 @@ public function testDenomalizeRecursive()
             'inner' => ['foo' => 'foo', 'bar' => 'bar'],
             'date' => '1988/01/21',
             'inners' => [['foo' => 1], ['foo' => 2]],
-        ], ObjectOuter::class);
+        ], ObjectOuter::class, null, ['datetime_format' => 'Y/m/d']);
 
         $this->assertSame('foo', $obj->getInner()->foo);
         $this->assertSame('bar', $obj->getInner()->bar);