In 2015, this improved process only happened for small parts of websites, and not all websites known in the index, but this has since increased in terms of coverage.
When it comes to rankings, in the original 2015 blog post, Yandex said that:
Taking into account the user interface, how information is displayed, and how it is served.
In 2018 Irstlena Pershina, an active Yandex public spokesperson on their webmaster blog recommended that the best-practice is for sites to use server-side-rendering (SSR) if they’re built on JS platforms.
You can read the support article here.
A general rule: there must be static content for the robot.
Irstlena Pershina, May 7 2018, 18:18hrs