How to specify platform when using oras push?

[Azathothas]

Hi, this may be a dumb question..

I read the docs: https://oras.land/docs/how_to_guides/manifest_config#arbitrary-os
So my config.json is:

{
    "architecture": "amd64",
    "os": "linux"
}

I pushed:

$ echo "hello" > hi.txt

$ cat config.json
{
    "architecture": "amd64",
    "os": "linux"
}

$ oras push --config config.json "ghcr.io/azathothas/oras/hello:latest" hi.txt
✓ Exists    hi.txt                                                                                           6/6  B 100.00%     0s
  └─ sha256:5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03
✓ Exists    application/vnd.unknown.config.v1+json                                                         51/51  B 100.00%     0s
  └─ sha256:c227293c458db8c541edd5561f03ad2689cc5f3ad0229a9feaf1f66a45c1deba
✓ Uploaded  application/vnd.oci.image.manifest.v1+json                                                   523/523  B 100.00%     0s
  └─ sha256:66654bcb933a025309a3d88d00b99a8d6b1f5601450d214a5fa58242db3d2497
Pushed [registry] ghcr.io/azathothas/oras/hello:latest
ArtifactType: application/vnd.unknown.config.v1+json
Digest: sha256:66654bcb933a025309a3d88d00b99a8d6b1f5601450d214a5fa58242db3d2497

However, this has no effect, and the resulting pushed image has no platform at all.
You can see it at: https://github.com/users/Azathothas/packages/container/package/oras%2Fhello

As per #1500 , I also tried:

$ oras push "ghcr.io/azathothas/oras/hello:latest" hi.txt --artifact-platform "linux/amd64"
Error: unknown flag: --artifact-platform

My oras version:

$ oras version
Version:        1.2.1
Go version:     go1.23.4
Git commit:     a0228556766b6276010d8feb937af512e8a50808
Git tree state: clean