Hello mendall.
Thank you for using Apple Support Communities. It sounds like you're unable to visit specific websites using Safari. Specifically, you're getting prompted "Content filter". If so, we should be able to help you with this specific issue. Allow us to assist.
Have you been able to check if you have Screen Time restrictions enabled on your device? this feature can prevent you from visiting certain websites. If you're not familiar with Screen Time, check out the resource below:
Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support
Review the section under "Prevent web content". Just in case, we have one more resource that explains more about filtering content:
Filtering content for Apple devices - Apple Support
We hope this information is useful. Cheers.