Why does my Apple mobile phone beauty camera display the handwriting of the beauty camera?

That's the watermark that comes with the beauty camera. When you send these watermarked photos, you also achieve an advertising effect, but the watermark can be cancelled.

Watermark cancellation step of extended beauty camera

Turn on the beauty camera and click the photo button.

2. Click on the three dot icons in the upper right corner.

3. Click the gear icon in the upper left corner.

4. Turn off automatic watermarking, and there will be no watermark in future photos.