How do I stop my iPad from searching cell signal?

The cellular update is probably unrelated to your general Software Update issue.

To resolve the cellular update error, go to Settings ➜ General ➜ About, it should initiate the cellular carrier settings update from there.

Manually update your carrier settings on your iPhone or iPad - Apple Support

Once that is done, you can try to update your iPad again.

If it has already downloaded the update and cannot apply it, you may need to delete it from the iPad and attempt to download it again.

Go to Settings ➜ General ➜ iPad Storage and look for the update, then delete it, restart the iPad and try to update again.

Starting at the beginning, the tags appended to your post suggest that you have an iPad Air2. The Air2 is capable of update to iPadOS 15.7.8; the Air2 does not support iPadOS16.

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 (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 15.7.8

Newer models are all able to be updated to the current version, iPadOS 16.6

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

If your iPad is capable of update to a more recent version of iOS/iPadOS than is currently installed, these support pages outline both the available methods by which the update can be performed - and troubleshooting should you experience difficulties:

Update your iPhone, iPad or iPod touch – Apple Support

If you can't update or restore your iPhone, iPad or iPod touch – Apple Support

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

iOS update and restore errors – Apple Support

Be aware that while an iPad may be capable of update, in some circumstances, such as with the situation that you deacribe, you may need to use a computer to perform the update. To do so, you will need access to either a Windows PC (with iTunes for Windows installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of MacOS). Ensure that your installed version of iTunes has been updated to the most recent version; the essential device drivers are included.

Download and use iTunes for Windows – Apple Support

Update to the latest version of iTunes – Apple Support

Update software on iPhone, iPad or iPod touch in iTunes on PC - Apple Support

Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

If you have a beta profile installed, ensure this has been removed from your iPad - as, otherwise, installation of production software updates may be inhibited. This support page provides the necessary information to remove the beta from your iPad:

How to uninstall iOS beta software - Apple Support

You should note that for your iPad to install an available update, its battery must be charged to at least 50% capacity - and/or be connected to its Power Adapter. Similarly, the iPad can only be updated over a standard WiFi connection - or be updated by a PC or Mac using iTunes or Finder - over a USB connection.

If its a Wi-Fi only iPad it does not have sim card. It also would not have a Cellular option or Cellular Data option in Setting. The fact it has this, indicates it a Cellular iPad.

If its a Wi-Fi + Cellular iPad it will have at least a sim card slot, and maybe an installed sim card, it will search for a cellular signal if the sim card installed is valid.

You can try to remove the sim card if its there and should then just show a "no sim" message.

Otherwise, searching for a cellular signal is normal behavior for cellular iPads which yours appears to be given what you have mentioned.

It is just a genetic settings update not tied to a specific carrier in that case.