https://bravokeyl.com/get-theme-file-uri-and-get-theme-file-path/

get-theme-file-url-backwards-compatibility.php

if(!function_exists('get_theme_file_uri')){
  function get_theme_file_uri( $file = '' ) {
    $file = ltrim( $file, '/' );
    if ( empty( $file ) ) {
        $url = get_stylesheet_directory_uri();
    } elseif ( file_exists( get_stylesheet_directory() . '/' . $file ) ) {
        $url = get_stylesheet_directory_uri() . '/' . $file;
    } else {
        $url = get_template_directory_uri() . '/' . $file;
    }
    return apply_filters( 'theme_file_uri', $url, $file );
  }
}