Fatal error: Declaration of EntityReferenceLayoutItemNormalizer normalize must be compatible with EntityReferenceItemNormalizer normalize in EntityReferenceLayoutItemNormalizer.php on line 34

When ERL is installed on Drupal >= 10.4.x the above error is seen.

The solution is to change:

  public function normalize($field_item, $format = NULL, array $context = []) {

... to:

  public function normalize($field_item, $format = NULL, array $context = []): array|string|int|float|bool|\ArrayObject|NULL {

... in entity_reference_layout/src/Normalizer/EntityReferenceLayoutItemNormalizer.php

Will upload a patch in a second.

A