When the debug mode is enabled from wp-config.php then this message show and indicate the user that developer mode is enabled. you can disable your debug mode from wp-config.php for more details
https://wordpress.org/support/article/debugging-in-wordpress/
Next
Follow below root
Go to wp-content > themes > Leganic > framework > redux.config.php
Find this
dev_mode
and set the value true to false.
Click save changes.
Later, you will see that developer mode have disappeared.
