Hi, a few things are happening there.
First is a Site Settings, that is to enable or disable the e-mail confirmation, if you set to false, it will completely disappear the box (default is true)
Site Setting: Authentication/Registration/EmailConfirmationEnabled
The Content Snippet responsible for rendering that is the Profile/EmailConfirmation/WarningText, you can just change the text there if you need
You can access the Content Snippet by navigating to make.powerapps.com --> apps --> Portal Management
You will be able to find both Content Snippets and Site Settings there:
