iPhone 12 Pro Max is taking a long time to update.

To update over the air from the phone all of these requirements must be met:

• You need at least 10 GB of free storage for iOS 16 and later or 6 GB for iOS 15 or lower; more is better
• You must be connected to a Wi-Fi network (and not a personal hotspot) unless it is an iPhone that supports cellular 5G (12, 13, 14 or SE 3rd edition) and has a 5G network connection
• The phone must be charged to at least 50%, and preferably plugged in so it stays above 50% during the update
• The phone must not be in Low Power Mode
• The phone must not be connected through VPN, and it may be necessary to delete any VPN apps and VPN profiles
• The phone cannot be in Airplane mode and must have a cellular data connection
• You cannot still have a beta of a previous version installed on the phone
• You cannot have a previous version that was downloaded, but not installed - go to Settings/General/iPhone Storage to look; if you find an iOS installer, delete it

If you can't meet all of them you can still update using your computer.

I’m having the same problem, but in my case i switched to the iphone 15 and i want to give my 12 pro max to my daughter, i already transferred and deleted everything from the phone. I’ve been trying to update my 12 pro max to ios 17.1 since yesterday and it’s not doing anything more than “loading”. What can i do?

Follow the guidance in the Apple Recommended post near the top of this page.