ipad: Attempted backup to Mac OS Monterey: The selected device could not be found

Recently upgraded to a new 24" Mac running OS 12.2 Monterey. Connected iPad 2 (iOS 9.3.5 - the latest version it can run) via USB to backup for the first time (was previously regularly synced to old 24" Mac running OS El Capitan). Device was listed in Finder, was asked to "Trust" on both iPad & Mac which I accepted, but Mac (after a while of "Loading...") displays the message "The selected device could not be found". iPad is showing it is being charged and still displayed in Finder Sidebar but it's contents not showing for backup.

How do I fix this so that I can backup & sync my iPad?