@ModStart: 升级php到8.1.3版本后出现以下错误：

Warning: require(/var/www/html/mod/vendor/composer/../symfony/polyfill-mbstring/bootstrap.php): Failed to open stream: No such file or directory in /var/www/html/mod/vendor/composer/autoload_real.php on line 78

Fatal error: Uncaught Error: Failed opening required '/var/www/html/mod/vendor/composer/../symfony/polyfill-mbstring/bootstrap.php' (include_path='.:/usr/share/pear:/usr/share/php:/usr/share/pear:/usr/share/php') in /var/www/html/mod/vendor/composer/autoload_real.php:78 Stack trace: #0 /var/www/html/mod/vendor/composer/autoload_real.php(61): composerRequire308896d8923435c0925d7aa5119b7e90() #1 /var/www/html/mod/vendor/autoload.php(7): ComposerAutoloaderInit308896d8923435c0925d7aa5119b7e90::getLoader() #2 /var/www/html/mod/public/index.php(34): require('...') #3 {main} thrown in /var/www/html/mod/vendor/composer/autoload_real.php on line 78

@ModStart: 前面的检测通过了，你们网站上环境要求不也是8.0就行了吗？

怎么我下载的文件里没有install.php这个文件？