iPadOS 18.3.1 killed 2 iPads

Using a Mac or Windows PC to perform a system software update, when device storage is insufficient, can indeed be helpful. Using this method allows the update package to be downloaded, unpacked and verified on the computer before installing the update on the target device.

Installing directly requires significantly more free space - as the package is initially downloaded, unpacked and verified on the target device - and still requires free space to actually install.

Notwithstanding the above, consistent failure to update using your Mac suggests that something is amiss with the Mac computer.

I've had a terrible experience with the IPadOS 18.3.1 update. My IPad's screen went completely grey despite the device clearly still being on and being picked up by laptop. Then three quarters of the screen came back, disappeared again, then it worked for a bit and then back to three quarters of the screen. Took in to an IStore, which recommended I replace the device, because it's a "hardware" issue only for it to work the next day again. Now I'm sadly stuck again with only three quarters of the screen working.

iPadOS 18.3.1 is stable. While there will always be isolated instances of difficulties installing any update, there are no widespread issues with iPadOS 18.3.1.

Given that you have consistently unsuccessfully updated multiple iPads - and consistently rendered each unusable - it may be reasonable to question your methodology in performing the update.

Is there a specific reason to avoid performing an system software update directly from iPad settings - as opposed to attempting (and failing) to successfully update the devices using your Mac computer?

You’ll find guidance for troubleshooting error #9 here:

If you see error 9, 4005, 4013, or 4014 when you restore your iPhone, iPad, or iPod touch - Apple Support

my iPad air 4th gen now has constant issues in nearly every app where I have to type, the cursor goes everywhere and I can only do emails on my iphone 16 which has also got issues. I cannot use Youtube properly as the video constantly fast forwards and I cannot stop this. What is going on? rebooted both. what a buggy ios!!!

Excellent news. I'm delighted to learn that your iPad is again up-and-running.