10 files declare their use of Routes in Drupal 9

DefaultExceptionSubscriber.php in core/modules/jsonapi/src/EventSubscriber/DefaultExceptionSubscriber.php

EntityReferenceFieldNormalizer.php in core/modules/jsonapi/src/Normalizer/EntityReferenceFieldNormalizer.php

EntityUuidConverter.php in core/modules/jsonapi/src/ParamConverter/EntityUuidConverter.php

jsonapi.module in core/modules/jsonapi/jsonapi.module

Module implementation file.

Relationship.php in core/modules/jsonapi/src/JsonApiResource/Relationship.php

RelationshipRouteAccessCheck.php in core/modules/jsonapi/src/Access/RelationshipRouteAccessCheck.php

ResourceObject.php in core/modules/jsonapi/src/JsonApiResource/ResourceObject.php

ResourceResponseValidatorTest.php in core/modules/jsonapi/tests/src/Unit/EventSubscriber/ResourceResponseValidatorTest.php

ResourceVersionRouteEnhancer.php in core/modules/jsonapi/src/Revisions/ResourceVersionRouteEnhancer.php

RoutesTest.php in core/modules/jsonapi/tests/src/Unit/Routing/RoutesTest.php