Does anyone know where in the console we can disable optimized search in v6.5.0?
Read this:
https://docs.splunk.com/Documentation/Splunk/6.5.2/Search/Quicktipsforoptimization
To turn off optimization for a specific search, the last command in your search criteria should be
|noop search_optimization=false
limits.conf has a switch that you can and should set to disabled in 6.5.0:
[search_optimization]
enabled = <bool>
https://answers.splunk.com/answers/465888/if-youre-running-650-you-should-disable-search-opt.html
If you are asking about the search assistant (compact vs. full mode), it is in Account Settings > Search > Search Assistant. See Help building searches in the Search Manual for more information.
If you are asking about syntax highlighting, you can disable it in the same account settings. See Help reading searches in the Search Manual for more information.
The Search Manual also includes two topics about optimizing searches (not what you asked about, but I am adding the info here for people who might stumble on this topic in the future):
What exactly do you mean by optimized search? The new syntax highlighting? Or autocomplete?
If its syntax highlighting then it is under each accounts settings. You can choose between 3 styles.