How to get rid of Interlace artifacts in output video

In most cases, if you have set your Video Mode to a progressive format, deinterlacing will happen automatically. If your video mode is “Automatic” and you happened to open an interlaced clip first, then your video mode might be interlaced. I recommend to set the video mode explicitly to exactly the mode you want to output.

As @shotcut mentioned, deinterlacing might be skipped if the interlacing is not detected in your source clip. This is rare. But if it happens, you can override it in the clip properties.