"The issue of the disabled delete button."

As Kylee says, this feature only allows you to delete what is in the timeline/sequence. Which means you must be in SEQUENCE/timeline view. In the tutorial video, the Delete button is active because they are in timeline view. You can tell this by looking at the bottom left of the text panel. They have "Follow active monitor" checked, and you can see that the "Show program monitor transcript" is active.

When you switch to source monitor view, you no longer have the Delete button active.

I filed a Beta bug report based on my belief that this feature applies to source transcripts. But it does not. When you work with a source media transcript in source view, you can edit the text and use the Replace function, but that only modifies the transcript, it does not remove any of the clip itself.

Stan

I have same issue. Kylee's comment is just the step to do it, which is what we've seen in any tutorial. Problem is when I am at that stage, have selected a filler or a pause (it is highlighted in blue), it won't disappear when I click delete button on Mac. I can even right click and see the options like delete, ripple delete, ignore, etc. But clicking there does not work either.

Hi! It sounds like you might be trying to remove filler words or pauses from a source clip. Just like when you edit video, you can't delete parts of the original source, just what you put in the timeline. 

Add your video to the sequence. The transcript will automatically switch over to your sequence. Then you can delete all pauses or filler and cut/copy/paste in the transcript.