The bug is especially dangerous for locked HTML files as DTTG4 for some reason converts HTMLs into formatted notes after viewing them in the app or after adding via the Share Sheet menu (this was discussed previously in Html is treated as formatted note in DTTG 4 iOS):
Equally off topic: Where do you see the video? I tried three browsers and none of them displays anything. FF shows an error message, Chrome complains about a CORB error.