Can't Split a Track

I have Window 8.1 Audacity Version 2.3.0

I am new to Audacity and am preparing my first track. I am trying to split a track so I can insert another recording to make a correction. I followed the instructions to the letter and track won’t split. However, I was able to split the track in another spot previously and had no difficulty splitting it. .
I decided to create another file to follow the same procedure and had no difficulty splitting the track. Returned to the other file, again followed the instructions to the letter and the track won’t split. Has anyone had this problem, and what did you do to fix it. Thanks

Which instructions?

I watched the following video between 1:50 and 2:50. The first time I did this everything worked. I have been trying to repeat the same procedure again by left-clicking with the mouse and the track won’t split. Opened up a new track and had no problems splitting the track.

https://www.youtube.com/watch?v=87McXcX_y-I&t=179s

You need to split the track first (see: https://youtu.be/87McXcX_y-I?t=100)
and then, switch to the Time Shift tool to drag the new clip.

Note that to be able to drag the audio clip, there has to be room (empty space) to drag it into. If you find that you can’t drag it to the right, it is probably because there is another audio clip in the way.