Various:

I have never heard that Japan agreed to attack the USSR. But it seems plausible that Hitler would have wanted them to. So he declared war on the US in hopes the Japanese would attack the USSR.

If those were his thoughts he erred by not insisting Japan give him a clear yes or no.

To me Hitler, by 1941, was driven more by passion than calculation. He craved excitement, the thrill of bold decisions and big stakes. And who knows what effects medications and astrology were having.

Often overlooked: The Japanese had actually tested Russia about 1937 in the Manchurian border area. It was a real war, but undeclared and short.

The USSR did poorly at first but Joe changed generals and sent in Zukov. Soon the Japanese were getting clobbered and withdrew. They showed no further interest in USSR territory.