Sealing heating pipe to wall

Hi!
How do I best seal the connection from the stove pipe (oil heating) to the wall connection/chimney?
I have read that there is a special silicone, but the silicone attacks certain metals like zinc and copper.
How can I tell what metal the pipe is made of, or are there better ways to seal it airtight?
When the heating turns on, you can smell it.
I took a few photos.
Maybe someone can give me a tip.

You should have a professional handle that, because you shouldn't be able to smell anything there - if only because of the chimney effect!

With me, nothing is sealed there because it simply isn't necessary - the stainless steel pipe fits inside the fireclay pipe like that...

It is a solid fuel chimney, but in this case that doesn't matter.

Possibly the draft is blocked?

I would first open the flap downstairs and look inside with a mirror to see if a bird has built a nest there. Because the chimney should be drawing.