There is absolutely no evidence of Putin’s involvement with Trump’s efforts to sabotage the post office. People are always looking for a convoluted, multilevel conspiracy they can claim credit for unraveling (muh Russia, QAnon, Pizzagate, etc.).
What’s happening here is pretty simple - Trump knows he needs to suppress votes to win, and if mail in voting makes it easier to vote, that becomes a lot harder. As such, he found a billionaire friend of his to make postmaster general and sabotage the post office so mail can’t reliably get anywhere on time. That alone should be enough to show how much of a threat to our Democracy Trump is. There’s no need to add conjecture about Putin to an otherwise simple and easy thing for the average American to understand.