An army in 1945 along the Bering Stait would have starved to death. There is no roads or any other transportation to keep an army supplied.
So on one hand you say the Red Army could not handle one over water crossing at the Bering Staits, an isolated area, to set up a army and supply beach head in N.America ..
But on other hand you say the Red Army could handle the many over water crossing to the many (well defended)islands of Japan and keep it army supplied?....