8 files declare their use of EntityDisplayInterface in Drupal 9

EntityDisplayBase.php in core/lib/Drupal/Core/Entity/EntityDisplayBase.php

EntityDisplayFormBaseTest.php in core/tests/Drupal/KernelTests/Core/Entity/EntityDisplayFormBaseTest.php

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

EntityDisplayWithLayoutInterface.php in core/modules/field_layout/src/Display/EntityDisplayWithLayoutInterface.php

field_layout.install in core/modules/field_layout/field_layout.install

Contains install and update functions for Field Layout.

LayoutEntityDisplayInterface.php in core/modules/layout_builder/src/Entity/LayoutEntityDisplayInterface.php

system.post_update.php in core/modules/system/system.post_update.php

Post update functions for System.

text.post_update.php in core/modules/text/text.post_update.php

Contains post update hooks for the text module.