Preferably you'd have a build server where you can use the build number. I use this to build my macOS application in GitHub Actions.

    [[ $GITHUB_REF_TYPE = "tag" ]] && MARKETING_VERSION=$GITHUB_REF_NAME || MARKETING_VERSION=$(git rev-parse --short HEAD)
    echo "Building $MARKETING_VERSION ($GITHUB_RUN_NUMBER)"
    agvtool new-version -all $GITHUB_RUN_NUMBER
    agvtool new-marketing-version $MARKETING_VERSION

Non-tagged build gives me "Building a3d4743 (54)", tagged build gives me "Building 0.3.1 (55)".