When something happened in the past and people keep telling you what happened...look into it. Look at what was being said at the time. Look up news articles being published at the time. They say Shokin was corrupt, were they saying it before Hunter Biden? Yes.
The last article on this list is a NYT article that actually discusses Hunter and is the closest you will find to a smoking gun. But it doesn't match the timeline. Burisma's investigation was ended before Shokin was fired.
Biden may have had ulterior motives for his activities in Ukraine, but he was over there pushing for these exact things before Hunter was hired. Maybe he somehow benefited from Shokin being fired, but the firing itself was on the up and up. I repeat: the firing itself is nothing.
Here's a custom search for news stories the time Shokin was fired:
https://bit.ly/3gc596x
Radio Free Europe
Scores of protesters have rallied in the Ukrainian capital, demanding the resignation of the country’s top prosecutor, who has been repeatedly criticized as an impediment to badly needed anticorruption reforms.
Kyiv Post
Deputy Prosecutor General Vitaly Kasko, who was given the job of cleaning up a corrupt, politically subservient and ineffective institution employing 15,000 prosecutors, quit on Feb. 15. In this farewell press conference, Kasko cited corruption and sabotage by General Prosecutor Viktor Shokin in combatting corruption and instituting the rule of law.
https://foreignpolicy.com/
Enough Carrots for Ukraine. Time to Break Out the Sticks.
Although Poroshenko finally sacked his widely hated prosecutor general, Viktor Shokin, this was primarily thanks to growing pressure from Western officials.
The Irish Times
EU hails sacking of Ukraine’s prosecutor Viktor Shokin
This one is probably the closest you are going to get to something that supports your beliefs:
NYTimes - Joe Biden, His Son and the Case Against a Ukrainian Oligarch
But Edward C. Chow, who follows Ukrainian policy at the Center for Strategic and International Studies, said the involvement of the vice president’s son with Mr. Zlochevsky’s firm undermined the Obama administration’s anticorruption message in Ukraine.
“Now you look at the Hunter Biden situation, and on the one hand you can credit the father for sending the anticorruption message,” Mr. Chow said. “But I think unfortunately it sends the message that a lot of foreign countries want to believe about America, that we are hypocritical about these issues.”