[[[ForeverAlone]]]

This is just US propaganda imo.

After Germany's surrender in Europe, USSR is able to redeploy its huge armies against the Japanese troops in East Asia.
For the battles for the NE Chinese cities (Puyi's Manchuria), the Soviets had  poured in 1.6mln troops against a smaller 700k and ill-equipped Japanese troops.
Of these 700K Japs, 600K were captured as POWs and forced into hard labour in Siberia.
Only 30K survived the harsh weather and environment there to return to Jap a few years later.

So without US dropping the nuclear bomb, Russia could have easily island hopped from the Kurils onto Hokkaido and then to the Japan main island.
Japan will surrender eventually - definitely not beyond 1949 when the Soviets also developed their first nuclear bomb - with half of Japan to USSR.
But US would not want to see that, a north-south Japan like Korea, so the hundreds of thousands of Japanese civilians in Hiroshima and Nagasaki were slaughtered by the US to  force a quicker surrender that favours the West. So only Kuril Islands that the Japanese had earlier captured from the China is under Russia's control present day.

but end of the day USA TAKE ACTION FIRST END WW2.