Is a Magic Keyboard of 11 inch compatible with an iPad of 10.9 inch?

The 11 inch Magic Keyboard is compatible with

iPad Models

• iPad Pro 11-inch (3rd generation)
• iPad Pro 11-inch (2nd generation)
• iPad Pro 11-inch (1st generation)
• iPad Air (5th generation)
• iPad Air (4th generation)

Guess I should have refreshed before answering.

Each Apple Magic Keyboard product webpage lists explicit iPad compatibility. If your iPad model is listed, its fully compatible.

For example - Magic Keyboard for iPad Pro 11-inch (3rd generation) and iPad Air (5th generation) - British English - Black

https://store.apple.com/uk/xc/product/MXQT2B/A is compatible with: