If you’re looking to translate only certain pages simply download and install the “Only translate certain paths” add-on like any other plugin: https://translatepress.com/download/3803/
This addon will allow you to add url paths that can be translated. Every other page on your website that doesn’t match that path will not be translatable.
This will work with the free version of TranslatePress and doesn’t have any drawbacks as far as SEO is concerned.
The settings are found in WordPress Admin -> Settings -> TranslatePress – Only Translate Certain Paths