The sound of the recorded video is deleted when the music is added to the video on YouTube

When uploading video on Youtube there is no possibility to add simultaniously music from Youtube library and keep the sound of the voice recorded. So, that both voice and music could be heard. It was possible before. Now, even if the music is added only to the end of the video, the voice is deleted (canceled) from the beginning (it is not low, there is just no sound at all). As a result, if I try to add music, I get a video without sound, but with music at the end of it. Before adding music the message appears: "please download the latest version". I have downloaded the latest version (24.0.0.186), but it still doesn't work.

Please, help me to sort out this problem!