Tinycam would be an app on the Firestick you open to use it, close it to open a different app (Youtube, Amazon Prime, Peacock, etc.)
Same with Onvier in case TC doesn't work out.
Try this "How to" :
https://www.howtogeek.com/336602/how-to-sideload-apps-on-the-fire-tv-and-fire-tv-stick/...