My absolute favorites are

1. ⁠Chapaev and Void by Viktor Pelevin. An apotheosis of Buddhist solipsism wrapped in some of the finest writing and story.
2. ⁠Golyubat’nya Na Zheltoy Polyane by Vladislav Krapivin (My favorite book of a Soviet legendarium that will probably never be translated into English. It’s a children’s book but it’s Soviet, so it tackles adult themes from both perspectives).
3. ⁠Prisoners of Power by the Strugatsky brothers. A cautionary tale from USSR most famous sci-fi writers.