"Undefined Variable" Error after Site Migration

CodeIgniter 3 are compatible with PHP 7.3 and users have also tested it with success on PHP 7.4.

If that error message are correct you have an error message regarding a database query. result() can't run without an database object. So I guess you didn't install it correctly. You have configured the database connection?

that's what driving me nuts. the mysql server (mariadb) runs. sql dump restored, privs restored, i can connect to it via mysql, using the same credentials and do everything. also no error messages in the mariadb logs. 

ofc changed the database.php (there was just a new password to enter)

but it still looks like the sql query is exactly what is failing.

it also show error messages if the tables don't exist. (i tried once, after i created the database and the credentials, but didn't yet import the sql dump). so the connection apparently to the mysqlserver apparently works. but there is no difference in the data, between the original mysql server and the imported dump. what on earth is going on here