Variable groups with YAML templates

Question

I want to use variable groups that are referenced in my template code. It wont allow me to reference groups in the template, or in the stages

Here is my pipeline code

trigger:
  batch: true
  branches:
    include:
    - main

pool:
  vmImage: ubuntu-latest

stages:

# Lint the Bicep file.
- stage: Lint
  jobs: 
  - template: pipeline-templates/lint.yml
    parameters:
      serviceConnectionName: AzureBicep

# Deploy to the dev environment.
- template: pipeline-templates/deploy.yml
  parameters:
    environmentType: Dev
    environmentShortName: dev
    resourceGroupName: rg-bomsup-dev-westeur
    serviceConnectionName: bom-supplier-deployment-CustomTools-Dev


# Deploy to the production environment.
- template: pipeline-templates/deploy.yml
  parameters:
    environmentType: Production
    environmentShortName: prod
    resourceGroupName: rg-bomsup-prod-westeur
    serviceConnectionName: bom-supplier-deployment-CustomTools-Prod

And here is the contents of deploy.yml (where I need to reference differnt variable groups for each environment)

parameters:
- name: environmentType
  type: string
- name: environmentShortName
  type: string
- name: resourceGroupName
  type: string
- name: serviceConnectionName
  type: string
- name: deploymentDefaultLocation
  type: string
  default: westeurope

stages:

- ${{ if ne(parameters.environmentType, 'Production') }}:
  - stage: Validate_${{parameters.environmentType}}
    displayName: Validate (${{parameters.environmentType}} Environment)
    jobs:
    - job: ValidateBicepCode
      displayName: Validate Bicep code
      steps:
        - task: AzureResourceManagerTemplateDeployment@3
          name: RunPreflightValidation
          displayName: Run preflight validation
          inputs:
            connectedServiceName: ${{parameters.serviceConnectionName}}
            location: ${{parameters.deploymentDefaultLocation}}
            deploymentMode: Validation
            resourceGroupName: ${{parameters.resourceGroupName}}
            csmFile: deploy/main.bicep
            overrideParameters: >
              -environmentType ${{parameters.environmentType}} -environmentShortName ${{parameters.environmentShortName}}

- ${{ if eq(parameters.environmentType, 'Production') }}:
  - stage: Preview_${{parameters.environmentType}}
    displayName: Preview (${{parameters.environmentType}} Environment)
    jobs:
    - job: PreviewAzureChanges
      displayName: Preview Azure changes
      steps:
        - task: AzureCLI@2
          name: RunWhatIf
          displayName: Run what-if
          inputs:
            azureSubscription: ${{parameters.serviceConnectionName}}
            scriptType: 'bash'
            scriptLocation: 'inlineScript'
            inlineScript: |
              az deployment group what-if \
                --resource-group ${{parameters.resourceGroupName}} \
                --template-file deploy/main.bicep \
                --parameters environmentType=${{parameters.environmentType}} environmentShortName=${{parameters.environmentShortName}}

- stage: Deploy_${{parameters.environmentType}}
  displayName: Deploy (${{parameters.environmentType}} Environment)
  jobs:
  - deployment: DeployResources
    displayName: Deploy Resources
    environment: ${{parameters.environmentType}}
    strategy:
      runOnce:
        deploy:
          steps:
            - checkout: self

            - task: AzureResourceManagerTemplateDeployment@3
              name: DeployBicepFile
              displayName: Deploy Bicep file
              inputs:
                connectedServiceName: ${{parameters.serviceConnectionName}}
                deploymentName: $(Build.BuildNumber)
                location: ${{parameters.deploymentDefaultLocation}}
                resourceGroupName: ${{parameters.resourceGroupName}}
                csmFile: deploy/main.bicep
                overrideParameters: >
                  -environmentType ${{parameters.environmentType}} -environmentShortName ${{parameters.environmentShortName}}
                deploymentOutputs: deploymentOutputs

            - bash: |
                echo "##vso[task.setvariable variable=appServiceAppHostName;isOutput=true]$(echo $DEPLOYMENT_OUTPUTS | jq -r '.appServiceAppHostName.value')"
              name: SaveDeploymentOutputs
              displayName: Save deployment outputs into variables
              env:
                DEPLOYMENT_OUTPUTS: $(deploymentOutputs)

How do I achieve this?