To make the Siri Shortcut available please try the following steps:
1. Make a short test resting using Just Press Record (This ensures the shortcut will be registered in the system)
2. In the Shortcuts app, tap Create Shortcut, then Add Action
3. Now tap Apps followed by Just Press Record, then 'Make a new recording'
4. Tap 'Next' at the top of the screen (iOS14) or tap on the name of the shortcut at the top of the screen (iOS 15 / 16)
5. Enter a name for the shortcut (e.g. "Make a recording") - this will be the phrase you use to start recording via Siri.