I don't understand your question. What is meant by "2 beams to hide where shiplap sections meet."? Where are the beams located? What is going to be shiplapped?

Any structural elements should be designed by the engineer who designed the existing structure.

No shiplap in that ceiling it will make the ceiling feel even lower this type of ceiling construction never makes sense to me but you in no way should be adding fake beams either get your architect or designer involved too That kitchen ceiling is going to feel incredibly low BTW

Where a beam meets up with flat ceiling over kitchen.

Here's an idea:

What was the designer's idea?

Sorry I wasn’t clear. Structural beams are hidden. We needed to make lr ceiling flat in order to run ac etc. this is a small home on a slab. The width of room is 30 ft so we are using fake white painted beams to cover joint where shiplap meets up to hide the joints.

Ok. so "shiplap beam" and "shiplap sections" refers to ceiling paneling not a joint in a beam. If your carpenter can't make a smooth transition in the paneling you could add a flat 2x6 and wrap it with trim or paneling.

Sorry I don’t understand “shiplap” as most people on here seem to mean is tongue and groove so what do you need to cover any seams

Ship lap is not T&G. Shiplap boards have a rabbet cut from its edges and that allows them to overlap but stay flat. One rabbet is usually larger than the other so there is a slight gap iat the installed joint. But the biggest difference in the appearance is that shiplap paneling must be face nailed and T&G paneling can be blind nailed. T&G can also have a decorative v groove or bead at the joint.

The "seam" in question is where the paneling changes from sloping to a flat kitchen ceiling. Apparently the OP wants something between the two boards.

A simple sketch would have helped a lot.

A good finish carpenter could miter that seam appropriately without having to resort to the coverup of a faked beam hiding the drywall underneath. If no good finish carpenter is involved, there are bigger issues. If there’s no drywall underneath, that’s a still bigger issue to address than a fake beam.

Adding one or two 2x's on the flat with trim would look like the bottom of the beam that supportis the roof/ceiling. That would also allow the use of gypsum board at the kitchen ceiling.

Mitering the boards would be difficult to keep straight and is likely to open up with time.

If you cannot allow any simulated features in a building, you were born in the wrong century. That ship has sailed.

I believe the purpose of the beams is to hide the butt joint (seam).

The width of room is 30 ft so we are using fake white painted beams to cover joint where shiplap meets up to hide the joints.

The carpenter just needs decent table saw skills to make an acceptable scarf seam. It doesn’t need a disguise.

In addition to the skill of the carpenter the success of a joint at the change of plane depends on the thickness of the paneling. its finish and the uniformity of the rafters where they are supported by the existing beam. The other consideration is how you plan to minimize air transfer to the unconditioned attic with shiplap paneling.