Finding. The Cantonese template is {{tts yue_HK:Front}}, and it sits on the back side only.
How I checked. I read Anki 26.9.3's own source (aqt/tts.py). Matching is an exact string comparison between the tag's language and the voice's locale as say -v ? prints it. Nothing maps yue_HK to zh_HK. I then listed the voices on dogmatix (macOS 26.6.2):
- Sinji is listed as
zh_HK. - No voice is listed as
yue_*at all.
So on desktop Anki, yue_HK matches no voice. Anki shows a "no players found" tooltip and plays nothing. It does not fall back to a Mandarin or default voice. Writing {{tts zh_HK:Front}} would pick Sinji, since it is the only zh_HK voice there.