Open Settings
Tap Screen Time
Tap Content & Privacy Restrictions
Turn on Content & Privacy Restrictions
Tap Content Restrictions
Tap Web Content
Select Limit Adult Websites
Under Never Allow, tap Add Website
Enter the site you want to block
Tap Done
To block all websites except approved ones, select Allowed Websites Only
Add the websites you want to allow
To remove a blocked site, go back to Never Allow and delete it