Hello,
If Allowed Websites alone is not working as expected we recommend adding the web address that is an issue to Never Allow as outlined here: Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support
"Prevent web content
iOS and iPadOS can automatically filter website content to limit access to adult content in Safari and other apps on your device. You can also add specific websites to an approved or blocked list, or you can limit access to only approved websites. Follow these steps:
- Go to Settings and tap Screen Time.
- Tap Content & Privacy Restrictions and enter your Screen Time passcode.
- Tap Content Restrictions, then tap Web Content.
- Choose Unrestricted Access, Limit Adult Websites, or Allowed Websites.
Depending on the access you allow, you might need to add information, like the website that you want to restrict."
We hope this helps!
Take care.