While I don't doubt that there have been Russian agents attempting to interfere in US elections (and vice versa in the past, btw), I am not sure if I believe that Prigozhin is telling the truth here. He is clearly trying to puff himself up for the Russian nationalist crowd as the effective leader, perhaps because he thinks Putin will be either dead from cancer or otherwise out of power soon.

There is a strategy sometimes used in the US in which if you can get the "other party" (whichever one that is for you) to attack you more, your status is elevated with your own side. Prigozhin is, by this point, clearly making a play for the post-Putin leadership of Russia. He is boasting to Russians that he can influence US (and other) elections, but that doesn't actually mean that he can, any more than he can achieve battlefield success with the Wagner group in Ukraine. But, if it results in a bunch of western (esp. left-leaning) outlets vilifying him, it elevates his status with the Russian right.