There should be a rather large wire coming from the battery to the panel and fuse 1 inside it. From what I can see in the video it looks to me that connection is coming off of the solenoid connection with the nut on it and has a side bar going to the outside left of the solenoid. I can’t see the underside of that piece but I suspect that is where the connection point to the battery may be at. You might try removing that piece from the solenoid to check it out. Be sure to disconnect the negative battery lead first if you do that.
To sum things up and hopefully clear up any confusion here is where we stand. Through your testing you have proved there is a connection problem between the positive battery post and the main distribution panel under the hood. Connection from the battery always has a heavy wire connection to the starter solenoid and to the starter motor for the high current needed for the starter motor. There is also another smaller wire connection needed to supply power to the distribution panel which supplies power to all the electrical systems in the car. That wire also needs to be fairly large since it has to carry a lot of current. The wire connection can come directly from the battery post clamp or the starter solenoid connection since that ties to the battery also. In your case it appears the connection for the panel is tied to the solenoid end of the battery cable. The trouble is most likely within 4 inches of where you made the test in the video.