13 files declare their use of PageInterface in Page Manager 8.4

Page.php in src/Entity/Page.php

PageAccessTest.php in tests/src/Unit/PageAccessTest.php

PageBlockDisplayVariantTest.php in tests/src/Unit/PageBlockDisplayVariantTest.php

PageContextTestBase.php in tests/src/Unit/PageContextTestBase.php

PageEditWizard.php in page_manager_ui/src/Wizard/PageEditWizard.php

PageListBuilder.php in page_manager_ui/src/Entity/PageListBuilder.php

PageManagerContextEvent.php in src/Event/PageManagerContextEvent.php

PageManagerController.php in page_manager_ui/src/Controller/PageManagerController.php

PageManagerRoutes.php in src/Routing/PageManagerRoutes.php

PageManagerRoutesTest.php in tests/src/Unit/PageManagerRoutesTest.php

PageVariant.php in src/Entity/PageVariant.php

PageVariantAddForm.php in page_manager_ui/src/Form/PageVariantAddForm.php

PageVariantTest.php in tests/src/Unit/PageVariantTest.php