clip YouTube video with iMovie

That is correct. The splits need to be made separately. This is because you need to place the playhead at the point where you want to make the split, and the playhead cannot be in more than one place at a time. You can do Mark/Add Marker to mark the places ahead of time where you want to make your splits. Then go back and make a spit at each marker.

-- Rich

Are you asking how to split a clip that you have downloaded from You Tube?

Drag the clip into the timeline of an iMovie project, select it by clicking on it, and do Modify/Split Clip. The clip will split at the place where you placed the playhead.

-- Rich

You are very welcome. 😊

-- Rich