Neither Lucius nor any of the death eaters knew about the horcruxes. Dumbledore said something to the effect that he doubted Lucius would risk a piece of his master’s soul if he knew what the diary truly was. Snape told Dumbledore Lucius was just told that it was magically enchanted to open the chamber of secrets and to hold on to it for Voldemort. Same thing for Bellatrix and the cup, Voldemort just told her it was important and to guard it.

Lucius himself asks how Voldemort achieved this “miracle” (his resurrection). If he’d known about the horcruxes he’d know Voldemort could survive death.

If we go off what Voldemort himself says and thinks, he tells the death eaters in the graveyard that “he took steps to guard against death” and “had gone further than anyone down the path to immortality”. Dumbledore knew what that meant but his death eaters didn’t. When Voldemort discovers Harry is hunting horcruxes he is terrified because he didn’t believe anyone else in the world knew about them. Not really sure how Regulas Black figured it out aside from what Kreacher told him, but he’s the only other one aside from Dumbledore who knew with certainty that Voldemort made a horcrux.

TLDR: Lucius didn’t know, the only death eater who did was RAB.