2 ways to Remove ONLY_FULL_GROUP_BY in mysql server Temporary & Permanently. with phpmyadmin and by modifying the server configuration file
Simple steps to Install and MySQL, PHP 8.0, phpMyAdmin with Nginx on an Ubuntu 20.04 Server
Just like you, I was having problems with this error When $cfg['blowfish_secret'] is set, the configuration file will now require a secret passphrase. It should be 32 bytes long.
A 413 Nginx error occurred while uploading the database through phpMyAdmin. the requested entity was too large as per the error.