After rendering video with Shift M because that's the only thing that makes my preview screen acceptable even when I have a good computer, just done with trying 1000 things to make this program work smoothly I got double screen in preview and also some other weird things like, video plays when there is no video on a track and also I think it may be because of this black thing whyich occured after rendering, how to fix this?
https://gyazo.com/6e6e7bb508d3a2513413c2c7431c4458