I think Tucker's explanation for why he is doing the interview tells us exactly what we can expect from the interview itself.
Putin will explain why he was justified in invading Ukraine, that the accusations or war crimes are all false and in fact Ukraine is the one guilty of war crimes, why western sanctions are unfair and self-destructive for the West, how allowing Finland and Sweden to join NATO is an unacceptable provocation for Russia, and more straight up unchallenged Putin propaganda.
We will also get some discussion about the moral degradation of the West and why Putin and Russia are the champions of traditional western values. I know this because Tucker has parroted these lines before.
We won't hear about targeted assassinations and jailings of opposition and media figures, we won't hear about how awful the Russian economy is, we won't hear about actual losses in the war, and we certainly won't hear any honest thought about the current strategic position of Russia in Ukraine and how precarious it is or isn't. We also won't hear about internal Russian opposition to the war.
EDIT: Forgot to add, there will be one or two moments of conflict where Tucker gets to pretend he is asking hard hitting questions, but it will all be scripted and will result in zero new insights.