They are mostly ice crystals. But they form around soot from the exhaust. There is research into reducing those emissions to reduce contrails since they contribute to the greenhouse effect https://www.nasa.gov/news-release/nasa-dlr-study-finds-sustainable-aviation-fuel-can-reduce-contrails/
So the conspiracy guys are kinda correct that the contrails are bad, but once again for all the wrong reasons.
Well I don’t know what there USP is in world where OneDrive/Google Drive/iCloud exist. And there future plan is a focus on AI, so yeah, goodbye Dropbox is my guess