I just noticed this setting on macOS System Settings > Apple ID > Contact Key Verification (at the bottom):
>Verify who you are messaging with by comparing contact verification codes in person or over the phone. In conversations with people who also have contact key verification turned on, you will see a message if contact key verification detects an issue or is turned off.
jereees|2 years ago
>Verify who you are messaging with by comparing contact verification codes in person or over the phone. In conversations with people who also have contact key verification turned on, you will see a message if contact key verification detects an issue or is turned off.