Vibrato is a periodic variation heard in many sustained sung tones. Its rate, extent, onset, and stylistic use vary across singers and genres, so one visual shape is not a universal standard of health or quality.
Do not manufacture the effect by shaking the jaw, pulsing the abdomen, or forcing the pitch. Begin with a comfortable sustained note and listen for what the voice already does when the phrase is easy.
Compare a straight-tone opening with a released ending at a moderate volume. Record the result. The useful question is whether the choice is repeatable and serves the style, not whether it matches one exact rate.
A browser pitch trace may show movement around a center pitch, but it cannot determine why that movement occurs or diagnose tension, airflow, or laryngeal function.
Practise vibrato as a musical choice inside a phrase: where does it begin, how long does it last, and what word does it support? Different genres invite different answers.
If sustained singing feels painful, hoarse, unusually tired, or strained, stop rather than trying to unlock vibrato through more effort. Persistent concerns belong with a qualified professional.