The prompt
If your firm has it turned on, pressing record shows Start Recording? before anything is captured:
You are about to start recording audio for the project you have selected.
This will capture system audio. Ensure you have consent from all participants before recording.
Recording may be subject to your organization's compliance policies.
Start Recording proceeds. Cancel stops, and nothing has been captured.
You can turn it on or off yourself in Settings, under Recording. The toggle is Show Consent Dialog, described as "Ask for confirmation before starting each recording".
Saying it out loud
The prompt confirms you have consent. It does not obtain it. That still takes a sentence at the top of the call, and the plainest version works best:
I'm recording this so I can write it up accurately afterwards. Is that alright with everyone?
Wait for the answer. If anyone hesitates, stop recording and take notes instead.
Recording laws differ by where each person on the call is, not by where you are. Some places need everyone's consent, some only yours. Your firm will have a position on this. Follow it rather than working it out per call.
Questions
I never see a consent prompt.
Your firm has it switched off, or you have. Turn it on in Settings under Recording if you would like the reminder. Its absence does not change your obligations on the call.
Does Junior announce to the call that I am recording?
No. Junior records your computer's audio locally and does not join the meeting as a participant, so Zoom, Teams and Meet have nothing to announce and no recording indicator appears for anyone else. Nobody on the call knows unless you tell them. That is exactly why telling them matters.
The exception is sending Junior to a meeting, where it does join as a visible participant.