Hi bigc56apple,
We appreciate you reaching out for help with your iPhone and this video quality issue. Your iPhone should shoot phenomenal clear and clean video, so we'd love to help in any way we can, or will point you in the right direction if appears service is recommended.
To start, please let us know more about what's going on. Which version of iOS have you got installed on your device? This can be found under Settings > General > About.
Does this issue occur with all video you shoot using your iPhone, and each of its cameras? Or does it only occur with videos shot in low-light, or using certain cameras? For example, what happens if you shoot a video outdoors in daylight using the front-facing camera, then test with the rear Wide camera, and then zoom out to test again with the Ultra Wide camera?
While each iPhone has unique camera characteristics, are you able to compare videos shot on your iPhone 8 with videos from your iPhone 11, all directly on your new iPhone? This will help to verify that any apparent differences aren't due to viewing them on a different screen.
If you've got any kind of protective case or skin on your iPhone, please be sure to remove it for further testing, to ensure there isn't anything interfering with the sensitive camera components.
Also, we recommend ensuring the camera lenses are clean and clear of any obstruction. Here's a guide to help:
Cleaning your iPhone
We're here for you if you've got any questions.
Have a great day!