“Does always flying cause blood clots?”

Although recent cross-country flights are a common screening question for pulmonary embolism or deep vein thrombosis (two of the more common clinically significant blood clots), there’s little research to determine how much flying matters in the formation of clots. There’s only one study from 2007 that I’m aware of, titled The Absolute Risk of Venous Thrombosis
after Air Travel: A Cohort Study of 8,755 Employees of International Organizations by Kuipers et al.