Kind of amazed that this issue is not made easier after years.
In my use case i just need to get a list of all metafields, to know what the partner has created already, so i can update their content.
Getting all their metafields is a pain in the ass though.
Should be made possible to get all metafrields with a resource owner. ie. all metafields on a owner_resource=product, or variant or image whatever.