Hey there jaiden59,
Thanks for reaching out to the Apple Support Communities. We understand you're having issues with your iPhone not recording videos as expected, and we'd be happy to help.
To get started, we'd like to ask a few questions to help narrow down the issue. First, do you receive any error messages when the video stops recording? Do you have iCloud Photos enabled on your iPhone? If so, have you confirmed that you have enough storage space in iCloud to save the videos as well? You can check this by going into Settings > [Your Name] > iCloud > Manage Storage.
If you use iCloud Photos, and you notice that your iCloud Storage is getting low, give the steps listed in this resource a try that can help with managing your iCloud storage: Manage your iCloud storage - Apple Support
If your device and iCloud Storage looks good, what is the video quality set to when this issue occurs? For example, if it's set to record in 4k 60fps, what happens if you lower the video quality?
Does restarting your iPhone help with the issue, even if it's just temporary? If unsure, give that a try with the steps shown here: Restart your iPhone - Apple Support
Keep us updated on the results, and we'll continue from there.
Take care!