For the mp4 video, you do not need to use iframevideo , iframevideo is only required for videos hosted on Youtube or Vimeo.
The current shortcode : [video src="https://interlan.app/wp-content/uploads/2019/09/Intro.mp4" /]
should work perfectly. However, it is a mp4 video, so if the size is big then the video will be downloaded in the app and then played, so it can take considerable amount of time based on its size to load and play in the app.
It is recommended to create streaming videos for this.