What has happened to the fast opening of Quick Notes on my iPad (by swiping from the bottom right corner of the iPad screen)?

The feature has not been removed in iPadOS 17.x. It may be necessary, however, to reset the feature following update to iPadOS17.

If already configured, you may need to initially disable the corner-swipe gestures from iPad settings:

Settings > General > Gestures > 

• Allow Finger Swipe from Corner - set to OFF 
• Left | Right Corner Swipe - select both to OFF

Restart your iPad:

Force restart iPad - Apple Support

After restart, enable the corner-swipe gestures as required:

Settings > General > Gestures > 

Allow Finger Swipe from Corner - set to ON - unless you wish to restrict gestures to just the Apple Pencil

Left | Right Corner Swipe - select Quick Note or Screenshot as required

have you checked if it's still in settings->control center

for you to add, not with my ipad right now but it there for my iphone with ios17