Netflix is currently not available in Russia so unless the series was officially released on some other network in Russia, there is no official Russian translated title and the field should be empty.

Netflix screenshot with Russian translation: https://prnt.sc/t9Pj4dwcYNru

IMDb screenshot: https://prnt.sc/VneeNBpIotdY

Russia movies DB - Kinopoisk: https://www.kinopoisk.ru/series/4693201/

Wikipedia

Therefore, I think that this translation can already be considered partially official, and in the case of an official release in Russia with a different name, the title can be updated, but now title "Задача трёх тел" is correct

I know the show has a Russian translation on Netflix, basically everything on Netflix has one. But Netflix has not been available in Russia since March 2022.

The "Translated Title" field is for the first official translation; in other words, the title of the first—theatrical, physical, digital or TV—release.

Since Netflix is not available in Russia, unless the show was officially and legally released in Russia, there is no official Russian translated title according to TMDB rules.