Wow! I just discovered that I am having the very same issue since upgrading to Catalina. For several years now, I have had all of my family videos and photos synced between my iMac and my iPhone. I just now discovered that everything has suddenly disappeared from my iPhone. I don't know if it is because I was adjusting my iCloud settings in the System Preferences app earlier this afternoon or not.
But regardless, just now, I attempted several times to restore/sync all of my videos and photos back onto my iPhone -- a 256 GB XS Max running iOS 13.
After clicking on my iPhone's icon in the Finder window's sidebar, I choose "Photos" in the horizontal menu at the top of the iPhone's window in the Finder.
The option "Sync photos to your device from" is enabled, and the pull-down menu is set to "Photos".
The "Sync" option is set to "All photos and albums", and the "Options" option is set to "Include videos."
When I click on the "Sync" button in the lower right corner of the Finder window, the progress wheel next to my iPhone icon in the Finder sidebar starts to spin for barely a few seconds, apparently fails, and then I am presented with a small on-screen window informing me of which songs were not able to be copied to my iPhone.
I was already aware of these few troublesome songs; but that is NOT the point. I was NOT trying to sync my music. My music is ALREADY on my iPhone and appears to be okay. I was trying to sync my PHOTOS.
As I said, I tried to sync in the aforementioned manner several times, but all to no avail.
Then I noticed that there was a second option for "Pictures" under the pull-down menu next to the "Sync photos to your device from" option; so I chose that.
I again chose the options "All folders" and "Include videos".
However, the weird thing is, in the "Folders" window that is located below those options, the ONLY folder listed is "Lightroom". It is NOT even showing anything in HD/Users/My Name/Pictures/Photos Library/.
So, there is nothing I can even sync if I choose "Pictures" instead of "Photos".
If I go ahead and click on the "Sync" button anyway, the same thing happens as if I had chosen "Photos". In other words, the progress wheel next to my iPhone icon spins for a few seconds, and then I just get the same on-screen message regarding a few songs that cannot be synced.
I honestly don't know how this bug could have slipped past Apple before the release of Catalina. Personally, I consider it major.
I hope a fix is forthcoming soon.