Define a controllable high note
Control does not mean touching a note once. It means repeatable pitch, no obvious squeeze, and a clean ending. That edge can change day to day.
Do not turn high-note practice into throat force
If the throat tightens or you get louder just to climb, lower the key. High notes need breath, resonance, and pitch control together.
Move in small semitone steps
Move up from your comfortable range by one semitone or small interval at a time. Advance only after three stable repetitions.