First, it should not reboot itself, you will have to figure out what's going on. But looks like it managed to install all what's needed.

Second:

have you installed flatpak-runner? You are expected to install that as well, its Sailfish app. Now start in terminal (or from launcher)

flatpak-runner

It will show you the list of installed apps. Angelfish should be recognized and in that list. After that, Angelfish will be available in the icon list of the launcher