Install Flatpak: https://flatpak.org/getting.html

For the stable releases:

flatpak remote-add flathub https://flathub.org/repo/flathub.flatpakrepo
flatpak install flathub com.vinszent.GnomeTwitch

If this is your first installed flatpak you will need to restart your session for it to show up in your normal launcher. Alternatively you can run flatpak run com.vinszent.GnomeTwitch.

To update it in the future gnome-software will do this automatically or you can run flatpak update occasionally.