Can’t access iPhone or iPad files on Mac after iOS 18.4 update

Since upgrading my iPad mini (v5) and iPhone (12 mini) to iOS 18.4, the Files function no longer connects to any of my Macs, either over wifi or by USB. I can see both devices in the Finder on my 2013 MacBook Pro running Big Sur 11.6.7, but none of the files on them are visible, and if I try to copy a file in either direction through iOS Files, the connection never completes or shows any files or folders in a shared device, just the spinning loading animation that never goes away.

[Re-Titled by Moderator]