David Kimura PRO said over 1 year ago on Streaming Videos with Active Storage :
  that is happening because you're using StimulusJS 2.x and the video was recorded when 1.x was the stable version.

<%= content_tag :video, data: { target: 'video.player' } do %>

could be changed to 

<%= content_tag :video, 'data-video-target': 'player' } do %>


<%= content_tag :video, data: { video: { target: 'player' }} do %>