Hello, not sure what to look exactly in your video.
The flow should be called on some button click, then you assign the value to its parameter. Why are you trying to access the delete parameter from within the flow itself?
If you search for ‘You will see the $_GET parameter which we are using in the Server Action to pass the selected record ID. Select the dynamic data picker button:’ you will find where it’s referenced in the tutorial.
I am having same issue, just posted about it, while the code Teodor supplied does work in the flow editor, the problem is now on the delete button Dynamic Event, the param is not there in the Flow to link to the RecordID.