Backing up iPhoneX with Catalina

I have updated both my Mac and my iPhoneX to the latest software, and am attempting to back my phone up to my computer in preparation for my new iPhone that's arriving on Monday. I *keep getting* an error message when I try to perform the backup, though. Finder tells me that, with every attempt, the iPhone is disconnected from the Mac.

It's not, as you can clearly see in the attached photos.

I've tried turning off the screen lock on the iPhone, which didn't help. I'm not sure what else I'm doing wrong here, so I'm hoping one of you can correct me.