When did the first direct assassination attempt on a Soviet leader since Fanny Kaplan's assassination attempt on Vladimir Lenin in August 1918 take place?

The Wiki article agrees that the attack on Leonid Brezhnev in 1969 was the first "direct" assassination attempt since Kaplan. The assassin Viktor Ilyin was a soldier who disguised himself as a policeman to get close. Brezhnev's driver was killed; Brezhnev survived.

https://en.wikipedia.org/wiki/Attempted_assassination_of_Leonid_Brezhnev

Another possible answer (depends what you mean by "direct") is rogue officer Savely Dmitriev's attempt on Joseph Stalin in 1942. Unlike other attempts that fizzled early, Dmitriev managed to get a shot off on a government car, but too bad for him, he hit a different car in the motorcade.

https://www.gw2ru.com/history/1536-mysterious-assassination-attempt-red-square

Both of these incidents remained secret for years; you've gotta wonder if there weren't other attempts we haven't heard about.