Here is a fix for Thrive Architect which allows to import themes from thelandingfactory when attachments are stored on S3. https://docs.thelandingfactory.com/article/51-how-do-i-install-the-template-on-my-website

class-thrive-transfer-import.php

<?php
// wp-content/themes/thrive-theme/inc/classes/transfer/class-thrive-transfer-import.php

class Thrive_Transfer_Import {

    public function open_archive() {
        $this->zip = new ZipArchive();

        $file = $this->getLocalPath($this->archive_file); // <----------------- line added

        if ( $this->zip->open( $file ) !== true ) {
    }

      /**
     * Download the file to the tmp folder if it's stored remotely.
     * The use case is humanmade/S3-Uploads plugin.
     *
     * @param $file
     * @return string
     * @throws Exception
     */
    private function getLocalPath($file)
    {
        if (strpos($file, '//') !== false) {
            if (!$temp = tempnam(sys_get_temp_dir(), basename($file))) {
                throw new Exception( __( 'Unable to create tmp file in '.sys_get_temp_dir(), 'thrive-cb' ) );
            }
            if (!copy($file, $temp)) {
                throw new Exception( __( 'Unable to download the archive file from '.$file, 'thrive-cb' ) );
            }
            return $temp;
        }
        return $file;
    }
}

TCB_Landing_Page_Transfer.php

<?php
//wp-content/plugins/thrive-visual-editor/landing-page/inc/TCB_Landing_Page_Transfer.php
class TCB_Landing_Page_Cloud_Templates_Api {

    public function import( $file, $page_id ) {
        $template_name = $this->importValidateFile( $file );
        
        $file = $this->getLocalPath($file); // <----------------- line added
        
        $zip = new ZipArchive();
        if ( $zip->open( $file ) !== true ) {
            throw new Exception( __( 'Could not open the archive file', 'thrive-cb' ) );
        }


    /**
     * Download the file to the tmp folder if it's stored remotely.
     * The use case is humanmade/S3-Uploads plugin.
     *
     * @param $file
     * @return string
     * @throws Exception
     */
    private function getLocalPath($file)
    {
        if (strpos($file, '//') !== false) {
            if (!$temp = tempnam(sys_get_temp_dir(), basename($file))) {
                throw new Exception( __( 'Unable to create tmp file in '.sys_get_temp_dir(), 'thrive-cb' ) );
            }
            if (!copy($file, $temp)) {
                throw new Exception( __( 'Unable to download the archive file from '.$file, 'thrive-cb' ) );
            }
            return $temp;
        }
        return $file;
    }
}