Opening anything in another app is relatively easy when it's a big, 'name-brand' app such as YouTube. The only caveat is that it's link-based so in the case of YouTube specifically, you need to have uploaded your video there in order to generate a link. It can be private and still have a link attached.
So once you have a link to the video on YouTube, you add that to a hotspot in your showcase as a 'URL'. When doing so, there is a little tickbox below the URL field that says "Open outside Showcase".
This is the one we want as it will trigger the link to open not in a web browser, but directly in the YouTube app assuming it is installed. If not installed, the nice thing is that it will gracefully fall back to a browser link and open in the browser anyway. Sweet!
Other apps this works well for are things like Google Maps (so a Google Maps link will open in the app if the checkbox is ticked and Google Maps app installed). You can generate links from things like Spotify, Instagram, & Facebook as well and these will work similarly in a similar situation.
In addition to the above, remember that if you add an unrecognised file type to a hotspot, you may be able to prompt your device to open it in a particular app too.
For help with hotspots in general and other types of links or content, check out our handy article on how to add content to a hotspot.