You'll see an iOS 18.7 update, but that's not the one you want to select. Instead, just below that tap on Upgrade to iOS 26 ...

Apple has released iPadOS 26, the next major software update for iPad users. Here’s what’s new, compatible devices, and how to install.

Prepare your iPhone for iOS 26 with this essential guide. Learn how to back up, free storage, and avoid update issues.