How do I submit this to the Godot Asset Library?

The problem here is that there is a lot of stuff on the Github page that should not be downloaded.

Here is the solution.

This is an example of a .gitattributes file that results in the downloaded .zip including only the addons folder:

# Normalize line endings for all files that Git considers text files.
* text=auto eol=lf

# Only include the addons folder when downloading from the Asset Library.
/**        export-ignore
/addons    !export-ignore
/addons/** !export-ignore

I used that for this asset, and it works correctly: https://godotengine.org/asset-library/asset/2307

Reference:
https://docs.godotengine.org/en/4.2/community/asset_library/submitting_to_assetlib.html#recommendations

Select the Addons / Asset Packs tab in that section of the article.

The only problem is that it prevents downloading the whole repository. But someone created a utility that lets you download a single directory or file:
https://minhaskamal.github.io/DownGit/

Actually, a problem with that .gitattributes example is that it affects the behavior of git commands. For example, if I try to compare two commits, files outside of the addons directory are ignored.

Correction. That example uses the export-ignore attribute, which only applies to some git commands. It doesn't affect git diff, so it probably doesn't affect comparing commits in GitHub.

I'm looking into a potential solution: a GitHub Workflow Action.

By looking at some examples and experimenting, I succeeded in creating a GitHub Workflow Action that ignores .gitattributes and creates a .zip of the full repository when I create a release.

A problem is that the .zip has too many levels:
release-archive.zip
.... release-archive.zip
.... .... tmp/
.... .... .... tmp.YbXGREv3M9/
.... .... .... .... (repository files)

.github/workflows/create-release-archive.yml

name: Create Release Archive

on:
  release:
    types:
      - created

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
    - name: Checkout repository
      uses: actions/checkout@v3

    - name: Archive repository
      run: |
        # Create a temporary directory
        TMP_DIR=$(mktemp -d)

        # Copy repository contents to the temporary directory, excluding specified files/directories
        rsync -av --exclude={'.git', '.github'} . ${TMP_DIR}

        # Create a ZIP archive
        zip -r release-archive.zip ${TMP_DIR}

      # Upload the ZIP archive as a GitHub Release asset
    - name: Upload Release Asset
      uses: actions/upload-artifact@v3
      with:
          name: release-archive.zip
          path: ./release-archive.zip

Ideally, I'd like the name of the .zip to use the same convention that GitHub or the Asset Library uses when you download a .zip in the normal way, and for the .zip to contain one top-level directory that has that same name.

Also, the created .zip is not in an obvious place in the repo's page.

Here's the final, working GitHub Workflow script that does everything I wanted. When a new GitHub release is created, it adds a .zip asset to the release page, with a name that indicates the repository name and the version tag, and containing a top level directory with the same name, and the full contents of the repository, excluding the .git* files and directories.

name: Create Release Archive

on:
  push:
    # Only run this workflow if github.ref_name has the form "x.y.z".
    tags: ["*.*.*"]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout Repository
        uses: actions/checkout@v3

        # Repository name, with owner name removed using sed (Stream Editor).
        # Example: "octocat/octorepo" is converted to "octorepo".
      - name: Repository Name
        run: echo REPOSITORY=`echo ${{ github.repository }} | sed s'#.*/\(.*\)#\1#'` >> "$GITHUB_ENV"

        # Example: octorepo-1.2.3-full_repository
      - name: Archive Name
        run: echo ARCHIVE="$REPOSITORY"-"${{ github.ref_name }}"-full_repository >> "$GITHUB_ENV"

        # Example: octorepo-1.2.3-full_repository.zip
      - name: Make Archive
        run: |
          # Create subdirectory, which will be archive's top level directory.
          mkdir "$ARCHIVE"

          # Copy desired files into subdirectory, excluding the subdirectory itself.
          # rsync is used because it has an --exclude option.
          rsync --archive --exclude={"$ARCHIVE",.gitignore,.gitattributes,.git,.github} . "$ARCHIVE"

          # Make archive from subdirectory.
          zip --recurse-paths "$ARCHIVE".zip "$ARCHIVE"

      - name: Upload Asset
        uses: softprops/action-gh-release@v1
        with:
          files: '*.zip'

If you're a coding beginner, stay away from writing GitHub workflows. It will be a nightmare.

probably a typo and 'inisia' is supposed to be 'inicia'? Como inicia would mean 'How to start' or 'How does it start'