Creating an Azure DevOps release pipeline using YAML config only

So I am able to create YAML only build pipelines (some of which also include release steps)

And these now work very well. We also have a selection of release pipelines which were built using the classic tasks

What I am thinking now is creating release pipelines using pure YAML but I cannot seem to get going on this. Is it possible or are we now expected to use pipelines for both build and release?

Any thoughts or ideas please?

There's no separation between builds and releases (aka deployments) in YAML pipelines.

You can use stages that represent different parts of your development cycle (e.g. build or deploy) and additionally organize it by environment (e.g. Dev, QA, Production) - for example:

YAML pipeline:

trigger: none

pool:
  vmImage: 'ubuntu-latest'

stages:
  - stage: Build
    dependsOn: []
    displayName: 'Build'
    jobs:
    - job: BuildJob # regular job, no environment (or approvals) required
      displayName: 'Build Job'
      steps:
      - script: echo 'Building...'
        displayName: 'Build Step'

  - stage: DeployDev
    displayName: 'Deploy to Dev'
    dependsOn: Build
    jobs:
    - deployment: DeployDevJob # deployment job
      displayName: 'Deploy to Dev job'
      environment: 'Dev' # Approvers and other checks can be configured for the environment
      strategy:
        runOnce:
          deploy:
            steps:
            - script: echo 'Deploying to Dev...'
              displayName: 'Deploy to Dev Step'

  - stage: DeployQA
    displayName: 'Deploy to QA'
    dependsOn: DeployDev
    jobs:
    - deployment: DeployQAJob # deployment job
      displayName: 'Deploy to QA Job'
      environment: 'QA' # Approvers and other checks can be configured for the environment
      strategy:
        runOnce:
          deploy:
            steps:
            - script: echo 'Deploying to QA...'
              displayName: 'Deploy to QA Step'

  - stage: DeployProd
    displayName: 'Deploy to Production'
    dependsOn: DeployQA
    jobs:
    - deployment: DeployProdJob # deployment job
      displayName: 'Deploy to Production Job'
      environment: 'Production' # Approvers and other checks can be configured for the environment
      strategy:
        runOnce:
          deploy:
            steps:
            - script: echo 'Deploying to Production...'
              displayName: 'Deploy to Production Step'

In YAML pipelines, and as already mentioned in Shamrai's answer, it is recommend that you put your deployment steps in a special type of job called a deployment job. A deployment job is a collection of steps that are run sequentially against an Azure DevOps environment.

Different Checks and approvals can be configured for each environment.