Github action to extract current version from package.json, increment the version and create the branch before running `npm version`

Question

I'm currently writing an example set of workflows for a generic NPM based application. I'm currently working on creating a release branch which branches of Dev. This can be called via workflow_dispatch or repository_dispatch. The expected input is simply one of "Major", "Minor" or "Patch".

name: Create Release

on:
  workflow_dispatch:
    inputs:
      version_bump:
        type: choice
        description: "Update Major, Minor or Patch"
        options:
          - Major
          - Minor
          - Patch
        default: Patch
  repository_dispatch:
    types: [create_release]

    
      
env:    
 ...

jobs:
  create-release-branch:
    name: Create release Branch
    runs-on: [self-hosted, k8s-app-deploy]
    steps:

    - name: Validate Repo Dispatch inputs
      if: github.event_name == 'repository_dispatch'
      run: |
        case "${{ github.event.client_payload.version }}"
          Major)
          major)
            echo "VERSION=major" >> $GITHUB_ENV
            ;;

          Minor)
          minor)
            echo "VERSION=minor" >> $GITHUB_ENV
          ;;

          Patch)
          patch)
            echo "VERSION=patch" >> $GITHUB_ENV
          ;;

          *)
            echo 
            echo "::error title={Invalid Inputs}::{The inputs for the Repository Dispatch were wrong, needs to be Major, Minor or Patch}"
            exit 1
    - name: Validate Workflow Dispatch input
      if: github.event_name == 'workflow_dispatch'
      run: echo VERSION=`echo ${{ inputs.version_bump }} | tr '[:upper:]' '[:lower:]'` >> $GITHUB_ENV
    - name:  Check out code
      uses: actions/checkout@v3
      with:
        ref: "Develop"
    
    - run: git remote update

    - name: Set release verison
      run: |
        
    - run: git checkout -b release/$RELEASE_VERSION origin/Develop

The bit I'm stuck on is the step Set release version. To my knowledge, npm version can't create a new branch beforehand, nor would I want it to be there anyway, as I'd like to be able to create RC versions until we actually merge into main \ master and release the version.

My thought track is to

1. Extract the current version from the package.json,
2. Increment the correct number and set that as the $RELEASE_VERSION,
3. Create Release branch with release/$RELEASE_VERSION
4. Run npm version $VERSION
5. Push & create PR from release branch to main

I'll then have other workflows pickup from there.

My question is, how would you set the $RELEASE_VERSION variable?