You know what they say about opinions. Don’t give opinions, give some proof it’s a bird or bug. No mumbo jumbo. Whatever it is, it’s actually faster near the end than when it begins, otherwise, someone could point this out. No flapping wings, too straight of a line after turn. I’m going to give my opinion since everyone else is giving theirs. It would have to be CGI if it’s not some vehicle or something we don’t know. Show decisive proof. The posters of the video have nothing to prove. I came here thinking I was gonna see an explanation. Like everywhere else, nothing.
I believe that the video that I made demonstrates that the movement is consistent with a bug, or possibly a small bird if the speed and distance is increased. It's not mumbo jumbo, it's a simulation.
The object does not need to be "faster near the end" as this is simply the illusion of the apparent speed of the object getting greater, the closer it gets to the camera. My video has exactly the same effect and the object in it is moving at a pretty consistant speed. The appearance of it moving in "too straight of a line after the turn" is just the product of its rate of movement across the frame. With such a small number of frames of video where the object is very close to the camera, the movement appears straighter, as there is much less time for movement to take place (how much vertical movement would you expect in less than 1/4 of a second).
As for there being no discernable wings, if it's a bug then these would not be visible due to the very high rate at which they beat. In the case of the object in the OP video being a small bird, the object is very small in the frame (just 2-4 pixels) for most of the video, so again wings would not be discernable.
It is only in the last few frames that the object is close enough that bird wings might be seen, but the rapid movement across the frame, creates motion blur, that can remove detail such as beating wings.
Could it be CGI... sure. I could take my render set up, improve it by adding motion blur and better lighting, then slap it on top of some drone video. But that would take time, and someone to want to do it. What doesn't require any work or inclination is it being something natural like a bug or bird.