Why is my keyboard folio not connecting to my iPad Pro 10.5

Start here:

Use your Smart Keyboard Folio or Smart Keyboard with your iPad - Apple Support

Do you see any errors or warnings when connecting or attempting to use the folio keyboard?

If you see an ‘Accessory may not be supported’ alert - Apple Support

If you are using a Smart (folio) keyboard, this alert is typical of a faulty folio keyboard. The electrical connections that pass though the flexible fabric hinges typically fracture - this usually resulting in errors and/or an on-screen notification. If the keyboard has completely failed, you may not see any reported errors.

The Smart folio keyboard itself is not repairable. The only remedy for a damaged/failed or faulty keyboard is its replacement. If you are within your one-year limited warranty, you will need to contact Apple Support or your retailer.

You will find the Get Support link at top-right of this page. 

Alternatively, you can initiate a support case using the excellent Apple Support App. If not already installed on your device, the App can be downloaded from the App Store:

https://apps.apple.com/gb/app/apple-support/id1130498044

A further alternative is to visit the Genius Bar at your local Apple Store, where the technicians will be delighted to assist. When visiting the Genius Bar, a reservation is recommended:

Genius Bar Reservation and Apple Support Options - Apple