A1475 iPad Air Wi-Fi Cellular would not auto update some apps.

Your description suggests that you have a first generation iPad Air, iPad mini2 or an mini3. These are the only models of iPad can be updated to iOS 12.5.6.

Apple ended major update support for these models of iPad in September 2019 - although they continue to receive occasional “point” security updates, the most recent being released August 2022. These devices cannot be updated to iPadOS 13 (or any later major versions of iPadOS) as the internal hardware does not meet the minimum technical requirements (CPU capabilities and available RAM) for newer versions of iOS/iPadOS.

Some App developers have dropped support for iOS versions preceding iOS 13.x for technical reasons (often because APIs or software libraries upon which they rely have been updated in the new version of iPadOS, making their App incompatible with earlier versions). 

Whilst many App titles remain compatible with your iPad, if you want or need to access to Apps requiring the most recent versions of iOS, you’ll need to consider replacement of your iPad with a newer or current model that supports iPadOS15.

Whether or not you are able to update any iPad to a newer version of iOS/iPadOS will be dictated by the iPad model - and the currently installed version of iOS. You can find this information here:

Settings > General > About

Not sure which iPad you have? Identify your iPad model.

Here is a list of the highest version of iOS supported by the older models of iPad (for simplicity - “generations” are shortened to a number) that are restricted in their ability to be updated:

32-bit devices

iPad1 - iOS 5.1.1

iPad2, iPad3 and iPad mini1 - iOS 9.3.5 (WiFi Only models), iOS 9.3.6 (WiFi & Cellular)

iPad4 - iOS 10.3.3 (WiFi Only), iOS 10.3.4 (WiFi & Cellular)

64-bit devices

iPad Air1, iPad mini2 and iPad mini3 - iOS 12.5.6

iPad Air2, iPad mini4 - iPadOS 15.7.1

Newer models are all able to be updated to the current version, iPadOS 16.1

• iPad Pro (all models)
• iPad Air (3rd generation and later)
• iPad (5th generation and later)
• iPad mini (5th generation and later)

As for restoring from iCloud, you cannot restore a device backup that was created by a device that has a higher version iOS/iPadOS than is installed on the target device. If the backup was created by an iPad with iOS 12.5.6, the backup should succeed in being restored to an iPad with iOS 12.5.6 installed.

If you are unable to restore the correct backup to your iPad, these support pages may help with troubleshooting:

Restore all content to iPad from a backup - Apple Support

If you can't update or restore your iPad - Apple Support

iOS update and restore errors - Apple Support

Whatever you stored in iCloud should just as easily be retreived from iCloud.

It usually, just takes a little while longer to retrieve data from iCloud than it is to upload the data to icloud.

For iPad models with a Home button, do a simple hard reset/forced restart of your iPad by holding down both the Home and sleep/wake/power button simultaneously until your iPad goes to black and restarts with Apple logo, then release the buttons.

The age and model of your iPad should not hinder any efforts to upload or download data to or from Apple's iCloud online servers.

Good Luck to You!