You're still missing a step. If you apply a picture-in-picture filter, customize the shadow settings in the box to see if the shadow value is set. Also, some audio-visual software does have this situation. You need to go to "mask and chroma key"-"chroma key" to extract black with a straw and set the value to zero. Check it carefully. As long as you solve the problem, sometimes the tutorial is not necessarily very detailed. The software has already set some settings, and you don't need to do it or explain which one.