This was a mistake on Truman’s part which we’re still paying for. Japan was totally defeated at the time whether their army bosses knew it or not and there was no reason for Russian involvement.
I don’t think Stalin was going to ask for Truman’s permission to get involved.
Actually it was FDR’s doing. Truman had nothing to do with various of FDR’s “deals” like Tehran, Yalta, ...
The Russians soaked up much of the German threat which the UK and US would have had to confront later. It was a different time.