The way the "chemtrail" simply stops in an instant makes it look fake to me. If you've ever seen skywriting in action, the smoke (or whatever they use) doesn't instantaneously stop at a perfect flat edge. It tapers noticeably, as one would expect. Although at this distance it's somewhat difficult to tell, it still doesn't look right.

It's also strange that this appears to be a commercial airliner, which is not the choice I'd make if I was running a nefarious covert scheme. For one, all commercial flights are public record. You can track where each one is at all times. If they were disguising chemical weapons as passenger jets, it would be trivial to gather some very solid evidence. Discrepancies in flight paths, mysteriously empty planes, etc.

Third, this trail is coming out as one very thick trail. If they were trying to disguise chemicals as contrails - which are a very real, proven thing - they wouldn't make it look this way. Contrails start off as small, individual trails from the engines and join together as they disperse. Why would they release a chemtrail in such a blatantly conspicuous way when they could simply release it in a contrail pattern and immediately assuage all doubt?

My vote is for AI generated fakery created by someone who doesn't know how airplanes work. It's by far the most likely explanation for these very basic mistakes.