7 files declare their use of DateTimeInterface in Drupal 10

DateTimeIso8601.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/DateTimeIso8601.php

DateTimeIso8601NormalizerTest.php in core/modules/serialization/tests/src/Unit/Normalizer/DateTimeIso8601NormalizerTest.php

DateTimeNormalizerTest.php in core/modules/serialization/tests/src/Unit/Normalizer/DateTimeNormalizerTest.php

PrimitiveTypeConstraintValidator.php in core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidator.php

Timestamp.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/Timestamp.php

TimestampNormalizerTest.php in core/modules/serialization/tests/src/Unit/Normalizer/TimestampNormalizerTest.php

TypedDataTest.php in core/tests/Drupal/KernelTests/Core/TypedData/TypedDataTest.php