Deploy sp referencing app reg within module errors out

Bicep version
N/a, using AzureResourceManagerTemplateDeployment@3 in Azure DevOps Server 25H2 (on-premise)

Resource and API version
Microsoft.Graph/servicePrincipals@v1.0 combined with Microsoft.Graph/applications@v1.0

Auth flow
Automated. Service connection authenticates with/via app registration using a certificate towards Azure.

Deployment details
Correlation id: e48512ff-cb2c-4d2b-8fe8-5bd8f673b61f
Start time: 18-8-2026, 14:48:50

Describe the bug
When deploying, both defined in a seperate file/module, an app registration and service principal referencing the app registration's appId, it fails with: The language expression property 'appId' doesn't exist, available properties are 'displayName, uniqueName, identifierUris, api, appRoles, owners'.
When they are defined in a directly deployed bicep, all goes well.

To Reproduce
deploy.bicep:

// Left params out since not relevant.
module appRegistration './app-registration.bicep' = {
  name: 'appRegistrationDeployment-${depName}'
  params: {
    name: appRegistrationName
  }
}

app-registration.bicep:

// Left params out since not relevant.
resource appRegistration 'Microsoft.Graph/applications@v1.0' = {
  displayName: name
  uniqueName: name
}

resource servicePrincipal 'Microsoft.Graph/servicePrincipals@v1.0' = {
  appId: appRegistration.appId
}

Additional context
It seems like it has something to do with it being in a module. Using another name for the resource does not help either, tried that to be sure it was not related to that.

Reproduce the failure with deploy.bicep and app-registration.bicep using the Microsoft.Graph applications and servicePrincipals resources. Start by tracing how the application resource's appId is exposed and resolved across the module boundary. Done means the module-based deployment succeeds and the service principal receives the application appId.