When the feature of code-generation was introduced, the logic for converting the postman requests to code snippets was outsourced. Postman used 3rd party library to produce these converted snippets from an open-source GitHub repository.
Postman has now built its own code-generators since the previously used 3rd party library had a lot of bugs as it was not maintained well. We've introduced bug-fixes, support for two new languages (JS-Fetch and Powershell) and the ability to configure certain aspects of the generated snippet with the 'New Code Generation mode' flag enabled in Postman's global settings. This is available from version 7.2.1.
But, we haven't completely removed the old mode since we are still improving the New Code Generation mode.
You can switch on the "New Code Generation mode" by navigating to the settings
Now when you will click on the code button, a whole new modal will be opened.
To know more, refer to this link: https://github.com/postmanlabs/postman-code-generators