Can I change the alarm sound anywhere?
It’s a matter of changing alarm-clock-elapsed in the sound theme. It’s usually done by overriding things in .local/share/sounds/__custom/. See https://specifications.freedesktop.org/sound-theme-spec/sound-theme-spec-latest.html . Making this configurable via the UI is on the (long) todo list, if somebody wants to hack on that, let me know.