You just necro’ed a 2 year old post.
Errr, thats the purpose of a browser source in SLDesktop or OBS Studio.
Alert providers provide a URL to use as a browser source in the stated software.
I’m not sure what the issue is that you are facing?
If
should of read
Then the answer to the uservoice https://twitch.uservoice.com/forums/904711-extensions/suggestions/40301335-allow-overlay-extensions-to-overlay-the-video-on-m is there are a number of issues which might make this technically not possible on mobile platforms, let alone an issue with size and readability, and/or connectivity issues on mobile anyway.
and
With this being the third party developers support forum, the answer is to raise a uservoice and/or vote on an existing uservoice.