What's wrong with the video frame rate? If I have a high-speed photographic video with 60 frames per second, I use editing software to slow down (that is, make a video).

I see what you are talking about, which is commonly known as jelly phenomenon. It is reasonable to put high frame rate video into low frame rate projects, but it is not. For example, if the N system with 30 frames per second is put into the P system with 24.9 frames, jelly phenomenon will appear, which means it feels like projection. So the best way is to use as consistent a frame rate as possible in the same project.