The show/hide preview is not available on mobile. You can skip that step when posting from a phone.
Yup; since a mobile browser doesn’t have the preview option, you just don’t need to worry about it.
FYI …
The mobile browser UI does have a preview mode. Which, if you activate it while you’ve got a YouTube url all ready to go, will trigger the bug.
In the screenshot that @Fear_Itself posted 3 posts up, the icon at lower right that looks like a display screen on a desk stand is the preview button. Tap that and you’ll be looking at a preview. And if you have already added an embedded vid url, you’ll trip the bug. Oops.
While you’re in preview mode, that lower right icon changes to a pencil. Tap that to get back to input / edit mode and re-enable the onscreen keyboard.
As an aside, anyone asking for Discourse help needs to include whether they’re on a phone or a big screen. Details matter. Some of us never post on a phone and some of us always post on a phone. So it’s easy to forget that your “obvious” context is not what everyone else is doing or seeing.
True. I forgot about that. It needs to be initiated manually and isn’t automatic like a computer browser’s preview pane so I didn’t even consider that.
I also tested WYSIWYG mode to see if it tries to make a video preview and it doesn’t, it still just has a link, so it’s only the preview mode that is a risk on mobile.