@Bronislaw666
You are making 0 sense. if you make a black and white highlight texture it won’t have Any seams simply because of the texture.
Its exactly the same as having a full skin texture.
If you have seams on a skin texture, you probably just have to increase the UV percision on your mesh import.
A texture in it self does not - ever - cause visible seams, unless you specifically made seams on it.
Also, share the UV map of your character. Normally, the seam is behind the back in a T shape for most models. Nowhere near the armpit. So its even more unclear what “seam” you think will be generated from adding a specifix corrective texture.