Michele Zanotti Greetings & Welcome to Microsoft Q&A forum!
As mentioned in the documentation, Fine-tuning supports deploying a fine-tuned model to a different region than where the model was originally fine-tuned. You can also deploy to a different subscription/region.
The only limitations are that the new region must also support fine-tuning and when deploying cross subscription the account generating the authorization token for the deployment must have access to both the source and destination subscriptions.
{'error': {'code': 'LinkedAuthorizationFailed', 'message': "The client has permission to perform action 'Microsoft.MachineLearningServices/workspaces/models/read' on scope '/subscriptions/<redacted>/resourceGroups/rg-dev/providers/Microsoft.CognitiveServices/accounts/<redacted>/deployments/my-model', however the current tenant '<redacted-target-tenant-id>' is not authorized to access linked subscription '<redacted-target-tenant-id>'."}}
As per the error, please double check that the user account you are using to authenticate has the necessary permissions to access the linked subscription in Tenant B. You may also need to check if there are any network or firewall restrictions that may be preventing access to the linked subscription.
I'll also check and confirm if there are any further restrictions among the different tenants.