It’s not just the Note app, as far as I can tell, the mechanical buttons for Next Page/Prev Page have now been globally mapped automatically as volume controls.
UPDATE: I found a work around for some apps, like Microsoft Word, what you do is to set one of the NavBall features to “Use page-flipping key as volume key”: in fact, it does the opposite - it returns the physical page-flipping keys to page-flipping keys.
But it doesn’t work for Note… the only thing that seems to work are the < > virtual buttons on the top right of the menu bar on either side of the page numbers: eg “< 2/5 >” = tapping on the < > symbols still works, as does tapping and holding on the page number to jump to a specific page. But I hear what you’re saying, @salaligan, flipping through quickly seems to be gone as a feature.
So far in my experience only NeoReader works properly with the physical buttons, and its Settings do allow the user to set them under Button Settings.
The application settings used to allow the user to set this for each app, not anymore. Since volume is not a priority for most apps, I strongly urge Onyx to return the page turning buttons back to their original function in the next update.