Github workflow to render helm diff between pull request branch and main. Adjust path with *.yaml if doesn't work. Also take a look at awk, and adjust depth there, to base dir for helm app. It will add comment with diff. I'm using this with argocd

helm-chart-compare.yml

name: Helm Chart Comparison

on:
  pull_request:
    paths:
      - 'gitops/charts/**/*.yaml'

jobs:
  find-changes:
    runs-on: ubuntu-latest
    outputs:
      modified_charts: ${{ steps.detect-modified-charts.outputs.modified_charts }}

    steps:
      # Checkout the PR code
      - name: Checkout PR
        uses: actions/checkout@v4
        with:
          path: pr
          fetch-depth: 0

      # Install Helm
      - name: Install Helm
        uses: azure/setup-helm@v3

      # Detect Modified Helm Charts
      - name: Detect Modified Charts
        id: detect-modified-charts
        run: |
          #!/bin/bash
          cd "${GITHUB_WORKSPACE}/pr/"
          modified_chart_files=$(git diff --name-only origin/${{ github.base_ref }} ${{ github.sha }} -- 'gitops/charts/*.yaml')
          echo "Modified yaml files:"
          echo $modified_chart_files
          modified_charts=$(echo "$modified_chart_files" | awk -F'/' '{print $1"/"$2"/"$3"/"$4;}' | sort -u | jq -nRMc '[inputs | select(length>0)]')
          echo "Modified charts:"
          echo $modified_charts
          echo "modified_charts=$modified_charts" >> $GITHUB_OUTPUT
        working-directory: ${{ github.workspace }}/pr

      - uses: izhangzhihao/delete-comment@master
        with:
          github_token: ${{ secrets.GITHUB_TOKEN }}
          delete_user_name: github-actions[bot]
          issue_number: ${{ github.event.pull_request.number }}

  helm-diff:
    runs-on: ubuntu-latest
    needs:
      - find-changes
    strategy:
      matrix:
        chart: ${{ fromJson(needs.find-changes.outputs.modified_charts) }}
      fail-fast: false
    steps:
      # Checkout the PR code
      - name: Checkout PR
        uses: actions/checkout@v4
        with:
          path: pr

      # Checkout the main branch code
      - name: Checkout main branch
        uses: actions/checkout@v4
        with:
          ref: 'main'
          path: main

      # Render and Compare Helm Charts
      - name: Render and Compare Helm Charts
        id: render-diff
        run: |
          chart_diff=""
          chart="${{ matrix.chart }}"
          pr_chart_path="${GITHUB_WORKSPACE}/pr/$chart"
          main_chart_path="${GITHUB_WORKSPACE}/main/$chart"

          chart_name="$(helm show chart $pr_chart_path | grep -E '^name:' | awk '{print $2}')"
          echo "Processing chart: $chart - $chart_name"

          helm dependency update $pr_chart_path
          helm template $chart_name $pr_chart_path > pr_rendered.yaml

          helm dependency update $main_chart_path
          helm template $chart_name $main_chart_path > main_rendered.yaml

          raw_diff_output=$(diff --unified main_rendered.yaml pr_rendered.yaml|| true)

          # Filter out the unwanted fields
          diff_output=$(echo "$raw_diff_output" | grep -Ev "^(--- |\+\+\+ )")
          diff_output=$(echo "$diff_output" | awk '
            /^@@/ {
              if (print_section && !skip_section) {
                print section
              }
              section=""  # Reset section
              print_section=0  # Reset print_section
              skip_section=0  # Reset skip_section
              skip_line=0  # Reset skip_line
            }
            /^[-+]/ {
              if (/app\.kubernetes\.io\/version: |helm\.sh\/chart: /) {
                skip_line++
              } else {
                print_section=1
              }
            }
            {
              section = section $0 "\n"  # Append current line to section
            }
            /^@@/,/^$/ {
              if (/^@@/ && skip_line == 2) {  # If only version/chart lines are found
                skip_section=1
              }
            }
            END {
              if (print_section && !skip_section) {
                print section
              }
            }
          ' )

          if [ -n "$diff_output" ]; then
            echo "Differences detected in chart: $chart"
            echo "::group::Chart Diff - $chart"
            echo "$diff_output"
            echo "::endgroup::"
            chart_diff="$diff_output"
            echo "diff_exists=true" >> $GITHUB_OUTPUT
          else
            echo "No differences in chart: $chart"
            echo "diff_exists=false" >> $GITHUB_OUTPUT
          fi

          echo "chart_diff=$(echo "$chart_diff" | jq -Rs .)" >> $GITHUB_OUTPUT

      - name: Post Comment with Diff
        if: steps.render-diff.outputs.diff_exists == 'true'
        uses: peter-evans/create-or-update-comment@v3
        with:
          issue-number: ${{ github.event.pull_request.number }}
          body: |
            # ${{ matrix.chart }}
            ```diff
            ${{ fromJSON(steps.render-diff.outputs.chart_diff) }}
            ```

      - name: Post Comment - Diff Empty
        if: steps.render-diff.outputs.diff_exists == 'false'
        uses: peter-evans/create-or-update-comment@v3
        with:
          issue-number: ${{ github.event.pull_request.number }}
          body: |
            # ${{ matrix.chart }}
            :white_check_mark: No differences found.