In Ireland / UK crime clans like Kinahan are deeply involved in professional martial arts not only boxing.
In the US you had criminal promoters over decades like King etc. that influenced fights. Thats proven beyond a doubt.
In recent time imo the most obvious was paid of judges like Adelaide Byrd which sadly could not be proven simply as there is no criminal case that is researched.
Boxing definitely has still strong ties into organized crime. Would surprise me if that is different in Mexico, Thailand and especially Russia and former Sovjet countries.
sports mafia does exist in all sports were you can make money betting.
Regarding the Usyk fight imo the bias was that Saudi Arabia bought the fight and are biased for Fury. Thats not really corruption but a kind of permanent influence on all people involved judges etc to regard that if they want work in the future.
Klitschko did that with K2 Promotions . They influenced the fight not through corruption with paying of refs etc but pressuring them into favouring them ni the match. Doing that Wladimir was allowed his wrestling match vs Powetkin or could choose the smallest possible ring..etc.
I would call that kinda corruption but its not that clear. This imo also happens with all fights in Saudi Arabia.