Gitlab Docker Registry "Content Trust" feature is not working

Dear Gitlab community,

We'd like to sign by default all the Docker images tags that we produce before shipping them to their respective Gitlab registries. For that we'd like to leverage the Docker Content Trust feature.

While working on Dockerhub and Azure Container Registry it always fail on Gitlab with the following error:

export DOCKER_CONTENT_TRUST=1
docker push registry.******/myimage:latest
The push refers to repository [registry.******/docker_tests/myimage]
05c130886995: Layer already exists 
4ce2b6308c40: Layer already exists 
1188ed1e1e90: Layer already exists 
4b6af21c7b3e: Layer already exists 
eeee134c5ad5: Layer already exists 
03901b4a2ea8: Layer already exists 
latest: digest: sha256:d66964aa400a7317d2455a04426261f36cc7bcf60e7cfb653fafae94672c5bf2 size: 1587
Signing and pushing trust metadata
Enter passphrase for root key with ID 5210698: 
Enter passphrase for new repository key with ID 9f3796e: 
Repeat passphrase for new repository key with ID 9f3796e: 
Error: trust data missing for remote repository registry.******/docker_tests/myimage or remote repository not found: timestamp key trust data unavailable.  Has a notary repository been initialized?

I can't find any info on the Gitlab documentation regarding that feature. Is there something to activate Gitlab-side ? Is it supported ?

Thanks for your support.