The use of Ukrainian Airspace has been scattered
Although there are evidently Russian-issued no-fly NOTAMs out too, Ukrainian Airspace has been scattered by the decision of airliners.
International Flights From East to West and vice versa have been started planning mostly including Romanian and Turkish Air corridors for complete avoidance of Ukrainian airspace.

Due to the Upcoming crisis, Airliners flying across to the European destinations, Turkish and Romanian Airspace will be the cost-effective corridor, Increasing number of flights will trigger the resulting high volume of air traffic along with these air corridors.