How can I get FaceID on iPad Pro to stop asking for my passcode 'every' time I use it?

Apply available updates, if any. Confirm there is no debris blocking the camera, and remove any screen-protective film or protective case, and try again. Failing that, reset Face ID, and try again. Then use the Get Support link in the upper right, and discuss your options and alternatives with Apple.

Here are the steps that Apple recommends > If Face ID isn't working on your iPhone or iPad Pro - Apple Support

If Face ID does not recognize your face after 3 attempts, you’ll be recommended to enter the passcode. After 5 attempts of unsuccessful face recognition, you’ll be *required* to enter the passcode for privacy purposes.

Have you tried reseting your FaceID?

Settings > FaceID & Passcode > Reset Face ID