TL;DR: When attaching media to a conversation from the inbox on the web, mobile users can't view these media attachments inside the Canvas Student App.
Why have a mobile app if communication with students doesn't work like it does on the desktop?
Students use phones and phone apps a lot and Canvas is no exception to that trend.
I made a video using the media button and the students, whose default mobile "Inbox," can't see it. So, I had to specify in another message that to see the video they need to go through "Conversations" by way of our Canvas website (preferably by way of desktop, as I'm unsure all mobile browsers, though it worked for me, optimize for viewing the video message).
Also, no where in the documentation (that I could find after extensive searching) is it stated that media button material does not show up in the mobile app. "Conversations" documentation should state this. Also, if I make a video using the media button, then, ideally, there should be a message that reads, "Caution: Media-button videos do not show up in the inbox for mobile app."
And, yes, before someone says it, I understand that I can make a video and then link it to the message, but that is a workaround and, therefore, not as convenient as using the media button.
The mobile app is used regularly for "Conversations" and, therefore, "Conversations" should work the same way it does on the desktop version.