Why can’t My iPhone 7 install the latest download

Currently, the latest public release is iOS 15.5. What version of iOS do you have on your iPhone? What happens when you try to install a newer iOS? Do you see an error? The iPhone 7 is eligible for the latest iOS 15.5. See this, Update your iPhone, iPad, or iPod touch - Apple Support

If you are not seeing an error message, try these two support documents for additional help. If your iPhone, iPad, or iPod touch won't update - Apple Support or this one. If you can't update or restore your iPhone or iPod touch - Apple Support

I assume that you are talking about the latest update. Check these links...

Update your iPhone, iPad, or iPod touch - Apple Support

If your iPhone, iPad, or iPod touch won't update - Apple Support

Updating iOS: common issues and solutions - Apple Community