You may be seeing watermarks on your video in these 2 scenarios:

Watermarks are visible by default on the preview page.

Watermarks help you identify which libraries are the media in your video from. They also give you a preview of how your final video would look like if you chose to keep brand and username watermarks while exporting.

The watermarks are removed when you export the video.

Once you have subscribed to a paid plan, projects you exported before subscribing will still have the watermark on them.

You will need to go back to the original project and export it again after subscribing to a paid plan and make sure the below options are selected -