I learned from some time on the phone with an Adobe customer service representative that the solution to the problem was in System Settings > Privacy and Security > Files & Folders, where one finds the settings in the attached screenshot (which is from my MBP, running OS Tahoe 26.5, which has been tethering fine all along).
My wife’s MBP, which was not connecting to the camera, is running OS Tahoe 26.6.2 (and has been since before we started learning to shoot tethered). We found the setting for Removable Volumes to be off! Turning it on solved the problem; the tethering began to work immediately.
Not having known about that little corner of the operating system, and therefore never having gone into it to turn anything on or off, I surmise that when both our MBPs were running 26.5 (i.e., when our MBP’s were new) both had that setting turned on (i.e., presumably its default at the time). But thanks to my wife’s MBP having been automatically upgrading the OS for some time, at some step between 26.5 and 26.6.2 the default became for Removable Volumes to be off.
I believe all this would perfectly explain what I’ve experienced, although I suppose one never knows what’s happening in the nooks and crannies of different (or slightly different) operating systems. A representative at Apple support was very cordial and engaged in the matter but in the final analysis, after my being on hold for a few minutes, told me they didn’t have access to the kind of detailed information I was looking for, that is, at what step in going from Tahoe 26.5 to 26.6.2 the default for that Removable Volumes setting changed from on to off.
I’m thinking I’ll end my work on this matter for now and begin working with my wife to refine her approach to tethered shooting using her MacBook Pro.
Thank you, degrub, for staying with this.
