No hooks are triggered for the Embed view of H5P content, which is inconsistent with behaviours of other views and does not work as expected.
Please see https://www.drupal.org/project/h5p/issues/3031362 for more details.
The issue above does not mention the embed header scripts hook, though that one is also required.
I have cloned the h5p repository from GitLab (8.x-1.x branch) and pushed the changes into GitHub. This commit solved it for me (only the tags hook is currently being used, but others should also work well enough):
The solution might be missing something and it should probably be better to create some reusable code for both views, but it seems to be working wee enough for now.
It would be great if this would be fixed soon and released as part of RC15. I am more than happy to make any changes to the code so that it would be accepted and merged.