The phrase "almost exclusively concerning" is correct and usable in written English.
It can be used when discussing a topic or subject that is primarily focused on a specific issue or area, with only minor exceptions.
Example: "The report is almost exclusively concerning the environmental impact of the new policy."
Alternatives: "primarily focused on" or "mainly related to".
The parallel conference has been almost exclusively concerned with his inadequacies.
For Armitage, these were not fruitful years, as the college was then almost exclusively concerned with painting and graphic work.
The first half of the trailer is almost exclusively concerned with the entire history of human violence.
Simply Red interviews from the peak years are almost exclusively concerned with gourmet dining and lashings of guilt-free sex – journalists' pre-imagined outline of one man's obsessions laid bare time and again.
It happened to me with Conrad's Under Western Eyes, a text that for years I recalled as a novel almost exclusively concerned with an unrequited and ultimately unrequitable love.
This is basic endocrinology, Ludwig says, which is the study of hormones, and it is still considered radical because the low-fat dietary wisdom emerged in the 1960's from researchers almost exclusively concerned with the effect of fat on cholesterol and heart disease.
Though Marty's publications are almost exclusively concerned with linguistic matters, he lectured extensively in all areas of philosophy.
The study therefore makes a valuable contribution to the literature on crime and public transport, which at present is almost exclusively concerned with public transport in developed countries [see the contribution by Natarajan et al. (2015) this volume, on crime and public transport in El Salvador].
Yto Barrada's photography, film, and sculptural work is almost exclusively concerned with Tangier, Morocco.
The poorest among them were almost exclusively concerned with the issue of food: most workers spent nearly half their income on bread.
