The poisoning incident is famous because the investigative journalism group Bellingcat identified the FSB (Russian spy service) members who followed Navalny and went into his Tomsk hotel room to apply the Novichok … to his underpants. Then the FSB's toxin group was found, and the lead scientist (Konstantin Kudryavtsev) confessed.
What really made the news (besides the underpants), was that Nalvalny himself called that scientist pretending to be an angry superior demanding to know what went wrong. Kudryavtsev explained details of how and where the poison was given, how he cleaned up the hotel room … over the phone for 45 minutes. A 2020 CNN article Russian opposition leader Alexey Navalny dupes spy into revealing how he was poisoned explains it.
For more references there's the bottom of a Wikipedia page devoted to the incident: Poisoning of Alexei Navalny. To sum it up: his condition was an international incident, leading experts on chemical weapons were called in, who in mind-numbing detail concluded it was Russian Novichok nerve agent.