8 files declare their use of EntityFormMode in Drupal 9

DisplayModeUpdateTest.php in core/modules/field/tests/src/Kernel/DisplayModeUpdateTest.php

EntityDisplayModeTest.php in core/modules/field_ui/tests/src/Functional/EntityDisplayModeTest.php

EntityFormDisplayTest.php in core/modules/field_ui/tests/src/Kernel/EntityFormDisplayTest.php

EntityFormModeResourceTestBase.php in core/tests/Drupal/FunctionalTests/Rest/EntityFormModeResourceTestBase.php

EntityFormModeTest.php in core/modules/jsonapi/tests/src/Functional/EntityFormModeTest.php

EntityFormTest.php in core/modules/system/tests/src/Functional/Entity/EntityFormTest.php

EntityTypeTest.php in core/tests/Drupal/Tests/Core/Entity/EntityTypeTest.php

FieldUIRouteTest.php in core/modules/field_ui/tests/src/Functional/FieldUIRouteTest.php