https://stackoverflow.com/questions/74105053/typescript-multiple-functions-with-distinct-parameters - reproduction attempt

check.ts

export class InitEventArgs {};
export class ResetEventArgs {};

export class ItemsChangedEventArgs {
   public added: ReadonlyArray<any>;
   public removed: ReadonlyArray<any>;
   constructor(added?: ReadonlyArray<any>, removed?: ReadonlyArray<any>) {
      this.added = added || [];
      this.removed = removed || [];

   }
};

export type ApiEventType = 'init' | 'reset' | 'itemsChanged';
export type ApiEventHandler = (() => void)
   | ((e:CustomEvent<InitEventArgs>) => void)  
   | ((e:CustomEvent<ResetEventArgs>) => void)  
   | ((e:CustomEvent<ItemsChangedEventArgs>) => void);

export interface IApi {
   // ...
   addEventListener: (type: ApiEventType, listener: ApiEventHandler) => void;
   removeEventListener: (type: ApiEventType, listener: ApiEventHandler) => void;
   // ...
}

const api: IApi = {} as any; // no implementation required
api.addEventListener('itemsChanged', (e:CustomEvent<ItemsChangedEventArgs>) => { /* ... */ });