Safari cannot connect to the internet on iPhone 15 mini with iOS 17.6.1

Good afternoon, on my iPhone 15 mini I keep getting the message in Safari: Safari cannot open the page because your iPhone is not connected to the internet. The software version on my iPhone is iOS 17.6. 1 (21G93). I can use Safari on the internet via wifi. I can use KPN 5G via DuckDuckGo on the internet. I would like your response where it goes wrong and how I can solve this. Kind regards, René Hooft.

[Re-Titled by Moderator]