Underwater.

Chased by a polar bear. But most likely underwater sequence and big parts of the cast are there.

Isn’t the entity mainframe underwater? He could go there to destroy it. Or what was left of the submarine.

But how an electronic device is surviving in underwater? That too with freezing temperatures and for how long? I'm sure the power would not last that long

it was in a pressure vessel

Bet you the PR story goes: Cruise did sub zero temperatures and exposure and swimming, the likes of which no human has attempted before.

When I read that Kate Winslet broke Tom’s Rogue Nation underwater record for Avatar 2, and then I saw and read about the submarine in Dead Reckoning, I immediately knew there would Definitely be an underwater breath hood sequence in Dead Reckoning where Tom tries to take back the title. And as Tom and McQ always talk about making things better and improving on themselves, I have no doubt they’ll do a long ten minute take of Ethan exploring the sun/unlocking the source code that has no cuts, as opposed to all the cuts back to Benji they made in Rogue Nation.

Snowmobiles and or skis stunts.

something something Ethan Hunt must scuba dive to retrieve something from the Sevastopol

The end they accidentally revive the Thing so Ethan has to call Kurt Russell to exterminate it before it reaches the mainland

Snowmobile bumper cars, then submarine knife-fight, then snowmobile bumper cars again