You made that up and its completely false. The Soviets were not about to invade Japan. The Soviets had no real navy to speak of, few landing craft, and no experience in amphibious operations. The Soviets did invade Manchuria and were advancing rapidly on land. You may recall Japan is a collection of islands. You can’t get there staying on land.
Please get your facts straight. Only America had the capability of actually invading Japan and until August 1945 only America had actually fought the Japanese. The Soviet invasion of Manchuria was helpful in convincing the Japanese to surrender, but the two A-bombs were the critical factors. Even after that the Japanese war cabinet was evenly split and the Emperor needed to come cast the deciding vote. A coup by junior officers almost succeeded in reversing that vote.
Without the bombs, surrender would have been delayed months and hundreds of thousands if not millions more would have died.
You expect America to have given the Soviets a stake in post- war Japan as a thank-you prize for all the Soviets had done against Hitler? That’s just naive.
The Soviets were already violating the Yalta agreements. They were refusing to allow free elections in Poland and were installing subservient Communist regimes across Eastern Europe. Truman should have been much more confrontational sooner. Your view is that the Soviets get to oppress Eastern Europe as a prize for doing so much to defeat the Nazis. I doubt FDR would have agreed. He would have much tougher. His unconditional surrender policy on the Axis was not the product of a mind looking for compromise or negotiation.