Send Feedback to Google about new Google Sites
Tell Google directly your feature requests and bug reports from your own new Google Site
Send Feedback from new Google Sites
Open your new Google Site in the editor (you can't send your feedback to Google about new Google Sites from this website - you must send it from your new Site).
Use the three-dot More button towards the top right (see video on right/below)
Choose Help Sites improve
Enter your description of the feedback
If you wish to send a screenshot highlight the important focal points and blackout any personal information (or you can choose to not send a screenshot).
Use the Send button
If you want to see the past feedback you have sent directly to Google please visit Google Feedback.