One potential solution is to check the video format and settings when recording videos on your iPhone. Make sure you're using a compatible format and settings that are supported by your device and its software. You can adjust these settings in the camera app or video recording settings on your iPhone.
Another thing to try is to update your iPhone's software to the latest version available. Sometimes, software updates include bug fixes and improvements that can address issues with video playback.
If updating the software doesn't resolve the problem, you can also try restarting your iPhone or performing a soft reset. This can sometimes help to clear temporary issues or glitches that may be affecting video playback.
If none of these solutions work, you may need to seek further assistance from Official Apple Support or visit an Apple Store to have your device inspected by a technician. They can help diagnose the issue and provide recommendations for resolving it.