Hi there, crazzmf.
Congratulations on your new iPhone 12 Pro Max!
It appears that you're having a problem using the camera from the Lock screen of your iPhone. Any type of photo or video you try to take opens to a blank screen, and we're glad to help with this.
How to back up your iPhone, iPad, and iPod touch - Apple Support -- Be sure to have a recent backup of your iPhone before proceeding.
If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support -- Since restarting your iPhone seems to correct the issue for a time, we'd like you to reinstall iOS 14. Place your device in recovery mode using the steps provided. When you're presented with options, please choose "Update" and not "Restore". Once the process has completed, see if the issue has been resolved.
Feel free to get back to us with any questions or problems you may have.
Cheers!