How can I download iOS 16.6 on my iPhone 11 Pro Max?

only way to install ios on an iphone is this way

Update iOS on iPhone - Apple Support

your signature suggest that you have an iphone 11 iOS 18.5 (22F76) is the only signed ios versions available for that model

Since the iPhone 11 Pro Max is compatible with iOS 18, you can update to the latest release of iOS 18. For that phone, updates to iOS 16 or 17 are no longer available.

Karnalkar (Author)

Your model iPhone 11 Pro Max should be able to run iOS 18.x

and is also listed as Compatible with a range of iPhone products.

How to download iOS 18 - Apple Support suggested recent iOS

//support.apple.com/en-us/104985

(..iOS 16 is now outdated available in 2022 for specific models..)

About iOS 16 Updates - Apple Support

//support.apple.com/en-us/101566

iOS 16.7.11 (current step is here)

This update provides important security

fixes and is recommended for all users.

Unless you choice is to Try & Restore

an iPhone ~ to a level prior to iOS 17.

For information on the security content of Apple

software updates, please visit this website:

Apple security releases - Apple Support

//support.apple.com/100100

Want to get the Current Latest update or having issues updating?

How to download iOS 18 - Apple Support

//support.apple.com/en-us/104985

So rather than ask again if you've specific question

about an upgrade to later iOS : see links to iOS18.x

since this current version with many are supported.