iPhone not going to sleep after getting notification.

I recently purchased the iPhone 16 which had the IOS18 out of the box and had a security update which I did update. Post that whenever I have my screen locked and I get a notification, my screen stays turned on and never turns off even after several minutes (I have kept the sleep duration to default - 30 secs ) I tried changing it and testing but it doesn’t work - it never sleeps until I manually click on the button for it to sleep.