Renaming system directory on EE6/7

On EE6/7 accessing the back-office via renamed system directory is no longer working for me:

“Your system folder path does not appear to be set correctly. Please open the following file and correct this: index.php”

In one occasion I had a clean install and followed the usual practice to rename system directory. https://docs.expressionengine.com/v6/installation/best-practices.html#increasing-security

In another instance I upgraded from EE5. got the same result.

$system_path = ‘./myadminarea’;

What am I missing? Besides the index and admin php files where else I can tell EE to understand that new system directory name?

Thx.