Have you followed the instructions Verify repository client with certificates | Docker Docs, and added the subfolder registry-1.docker.io and placed the cert inside the folder with a filename that ends on .crt?
It should look like this /etc/docker/certs.d/registry-1.docker.io/ca.crt.
Though, this only handles docker engine to registry communication. Every container that needs to make https calls to the internet needs to be modified as well.