11 files declare their use of ContentEntityForm in Zircon Profile 8

AccountForm.php in core/modules/user/src/AccountForm.php

Contains \Drupal\user\AccountForm.

BlockContentForm.php in core/modules/block_content/src/BlockContentForm.php

Contains \Drupal\block_content\BlockContentForm.

BookOutlineForm.php in core/modules/book/src/Form/BookOutlineForm.php

Contains \Drupal\book\Form\BookOutlineForm.

CommentForm.php in core/modules/comment/src/CommentForm.php

Contains \Drupal\comment\CommentForm.

EntityTestForm.php in core/modules/system/tests/modules/entity_test/src/EntityTestForm.php

Contains \Drupal\entity_test\EntityTestForm.

FeedForm.php in core/modules/aggregator/src/FeedForm.php

Contains \Drupal\aggregator\FeedForm.

MenuLinkContentForm.php in core/modules/menu_link_content/src/Form/MenuLinkContentForm.php

Contains \Drupal\menu_link_content\Form\MenuLinkContentForm.

MessageForm.php in core/modules/contact/src/MessageForm.php

Contains \Drupal\contact\MessageForm.

NodeForm.php in core/modules/node/src/NodeForm.php

Contains \Drupal\node\NodeForm.

ShortcutForm.php in core/modules/shortcut/src/ShortcutForm.php

Contains \Drupal\shortcut\ShortcutForm.

TermForm.php in core/modules/taxonomy/src/TermForm.php

Contains \Drupal\taxonomy\TermForm.