I have a ipad mini 2 that is on ios 9.3.5 and I want to update it to ios 11 but there has not been a ios 11 update available for it in a long time. What do I do?

Are you sure it’s an iPad mini 2, and not a first generation iPad mini? While the 2 can run iOS 11 (which is confirmed here https://www.apple.com/ios/ios-11/), the first generation can only be updated to iOS 9.3.5.

Check your model https://support.apple.com/en-us/HT201471 and if it is indeed a mini 2, you can troubleshoot the issue, but we need more info on how you’re trying to update, and what happens when you do. I’d start here though: https://support.apple.com/en-us/HT204204

Make sure it's an iPad mini 2 or later not Mini 1. A6X and A6 devices and earlier devices are incapable of running iOS 11 and later. iPad mini 1 has an A5 chip. To know your iPad's model; go to Settings > General > About then scroll to find Model and look up the model shown. If you got the iPad between September 2012 and September 2013 it's an iPad mini 1. If not it maybe a Mini 2. If it came with iOS 6 it's a iPad mini 1. If any of that didn't work then call Apple Support then ask what model it is. They may ask for an IMEI number or a Serial Number. To find both of them go to Settings > General > About then scroll to find one of them.

I hope that helped.

Your device is running the maximum version of iOS supported by the hardware. If you want to run apps that require iOS 11 you will need a new device.

tt2