The described behaviour - and the icons that you see - suggest that Apps have been offloaded from the iPad. While the corresponding Apps remain available for download, tapping the icon should reinstall the App.
However, if a compatible version of the App is no longer available, or has been withdrawn, you will be unable to reinstall the App on your iPad. When a compatible App isn't available for download, the error message that you see can sometimes be misleading.
For older models of iPad that are no longer supported (such as the iPad mini2 - limited to iOS 12.5.7), there is a very real risk that you may be unable to reinstall offloaded/deleted Apps, as some App Developers often only support the last two or three major versions of iOS/iPadOS. Sometimes a situation will occur where an older (i.e., compatible) version of an App may no longer be available.
For Apps that fail to reinstall, check their current minimum OS requirements. Search for the App within the Apple App Store; scroll down to the Information panel, then expand the Compatibility section to see the minimum OS requirement for the App.
If the available App requires a higher version of iOS/iPadOS than your iPad can support, you'll not be able to reinstall the App on your iPad.
The first generation iPad Air, iPad mini2 and mini3 can only be updated to iOS 12.5.7.
Apple ended major update support for these models of iPad in September 2019 - although they have since received occasional “point” security updates, the most recent being released January 2023. 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.
Whilst many App titles remain compatible with your iPad, if you want or need to access to Apps requiring the more recent versions of iOS, you’ll need to consider replacement of your iPad with a newer or current model that supports iPadOS 17.
For information, 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 (obsolete)
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 12.5.7
iPad Air2, iPad mini4 - iPadOS 15.8.2
iPad5, iPad Pro (9.7"/12.9" first generation) - iPadOS 16.7.7
(*) obsolete
Newer models are all able to be updated to the current version - iPadOS 17.4.1
- iPad Pro 12.9" (2nd generation and later)
- iPad Pro 11" (1st generation and later)
- iPad Pro 10.5"
- iPad Air (3rd generation and later)
- iPad (6th generation and later)
- iPad mini (5th generation and later)