open fireplace in the outdoor area, dimensions/size ratios

Hello,
this thread may not belong 100% in the planning section, but there is no really suitable subforum. Besides, it is about the planning to get the fireplace running.
I have previously searched through some craft forums but have not found a solution to my problem here.
It is probably about a poorly built open fireplace in a semi-open room:

The room is a freestanding room that can be opened completely on two sides, a kind of garden/leisure/grill/wind protection room. An open fireplace was built in it on a long wall. However, not really by a professional. It’s all abroad, after all.

Therefore, it is not about any DIN standards, regulations, ordinances, or other regulations, and it does not need any heating effect; the function is mainly a grill and coziness.

The fireplace is masonry, the opening to the room is 90 cm wide and 95 cm high, the chimney above is built inward with offset bricks and leads into a square chimney (also masonry) of 35 cm x 38 cm, which is 1.4 m high and has a cover with side openings.

And of course, this thing doesn’t work, it smokes everywhere, through the chimney but also into the room.

Here are the pictures:

Front view:

Looking diagonally upwards, the concrete beams are supposed to support the chimney:

View into the chimney, the chimney cap is 70 cm, the chimney itself 1.4 m:

Now I wonder whether the cross-section of the chimney in an open fireplace can be smaller than the air inlet, i.e., the open area?

Does the chimney opening, the outlet at the top, have to be the same size as the inlet area of the chimney? Or can it be smaller because of a cover against rain?

Is a damper needed in the chimney?

Does an additional fresh air supply through an extra opening at the back of the firebox help?

Is there a website on the internet maybe with standard construction types for open fireplaces, similar to how there are for wells, for example?

I would really immediately ask, hire, and pay a chimney sweep or fireplace builder, but believe me, there’s no such profession here, and I am really far away.

So already many, many thanks for any basic information about fireplace and chimney construction.

Hello, the best thing is probably to contact the local chimney sweep master. If you do not know his name, just look online under the chimney sweeps' guild. There you will find the appropriate contact person.

@ ansgarm74:

... It's all abroad anyway.

Therefore, it’s not about any DIN standards, regulations, ordinances, or other rules, nor does it need any heating effect; the function is mainly a grill and coziness.

...

I would really immediately ask, commission, and pay a chimney sweep or stove builder, but believe me, such a profession does not exist here and I am really far away

Thanks for the great tip "ansgarm74", but that really doesn’t help.

Believe me, there are no master chimney sweeps, guilds, Yellow Pages or anything like that here.