Try adding define('CONCATENATE_SCRIPTS', false); to your wp-config.php file just below the define('DB_HOST' line.
To do so, access your server via SFTP or FTP, or a file manager in your hosting account’s control panel (consult your hosting provider’s documentation for specifics on these), and edit the file with a plain text editor.
For details: https://ww.wp.xz.cn/support/article/editing-wp-config-php/#disable-javascript-concatenation