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See the video

In the video it is clear that the jet takes off and lands with all these 3 things "open/stretching out" (so it seems to fly just like that - not retracting them).

Here is Wiki on that model.

Code Complete
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1 Answers1

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The upper thing is a mirror for the WSO's (rear seater's) periscope. It gives that position some forward visibility when extended. Without it, I doubt that position could see the runway. There are several other Russian aircraft with periscopes.

The lower ones are speedbrakes.

Looking at the underside of the vehicle my speculation is that they interfere with the landing gear retraction, so are extended until that point. But if that's true, do they have to extend when the gear come down for landing? No idea. I can't think of another good reason for them to be open on takeoff.

A comment from ymb1 showed a very nice image of the doors/speedbrakes on wikimedia MiG-31 landing gear This shows that they need to be extended until the gear is retracted.

BowlOfRed
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    See the footnote I've written here, for why underside air brakes are useful. It helps with trimming for landing. –  Aug 28 '19 at 09:32
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    But then why are the air brakes extended for takeoff? I did not watch the video, but the questions says takes off and lands with all these 3 things "open/stretching out". – Bianfable Aug 28 '19 at 09:33
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    Mystery solved (I think): the air brakes double as landing gear doors (which would confirm your speculation). –  Aug 28 '19 at 10:09
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    Yes, or rather, the landing gear doors double as airbrakes. Because, why not? The extra drag at takeoff is insignificant for this aircraft. – Zeus Aug 29 '19 at 01:07