"The controller result claims to be providing relevant cache metadata, but leaked metadata was detected. Please ensure you are not rendering content too early. Returned object class: Drupal\\jsonapi\\CacheableResourceResponse."

Same patch that applies to the beta10 version that is the last version on PHP 7.4.

This shouldn't be necessary according to #3072076: JSON:API returns a CacheableResponseInterface instance for non-cacheable methods; causes unnecessary exceptions. → .

But, since we are using JSON API Resources, a CacheableResourceResponse is always returned... So I believe this should be fixed in JSON API Resources probably instead, leaving this opened for now.

Committed, still.

Automatically closed - issue fixed for 2 weeks with no activity.