How to change css poperty through webhook in wordpress

you are trying to return data from the PHP function showTheButton(). You are directly echoing js code inside the function, which will not be properly handled when returning data from the function.

JavaScript function to toggle button visibility

function showTheButton($dateofReturn, $reportType) {
    // Set a flag to indicate whether the button should be shown
    $show_button = false;

    // Check conditions to determine if button should be shown
    if ($dateofReturn && $reportType) {
        $show_button = true;
    }

    // Return the flag value
    return $show_button;
}

WordPress action hook for form submission

add_action('elementor_pro/forms/new_record', function($record, $handler) {
    // Make sure it's our form
    $form_name = $record->get_form_settings('form_name');

    // Replace 'reportGenerationForm' with the name you gave your form
    if ('reportGenerationForm' !== $form_name) {
        return;
    }

    // Extract submitted fields
    $raw_fields = $record->get('fields');
    $fields = [];

    foreach ($raw_fields as $id => $field) {
        // Sanitize field values
        $fields[$id] = sanitize_text_field($field['value']);
    }

    // Get report date and type
    $dateofReturn = isset($fields['reportDate']) ? $fields['reportDate'] : '';
    $reportType = isset($fields['reportType']) ? $fields['reportType'] : '';

    // Call PHP function to determine if button should be shown
    $show_button = showTheButton($dateofReturn, $reportType);

    // Add response data indicating whether button should be shown
    $handler->add_response_data('show_button', $show_button);
}, 10, 2);

In your js code, you can then check the value of the show_button flag and execute the necessary js code to toggle the button visibility

document.addEventListener('DOMContentLoaded', function() {
    var showButton = '<?php echo json_encode($show_button); ?>';

    // Check if the show_button flag is true
    if (showButton) {
        var button = document.getElementById('view-report');
        button.style.display = 'block';
    }
});