P: Fails to import photos and stalls out on macOS 10.15 Catalina

To expand on David's reply a bit, look down the left to Untitled (which is your memory card), click the arrow to expand and click on the DCIM folder to view the photos inside. There's two different ways of accessing the photos and the "devices" one is broken on Catalina but the other works.

And on the left, are you clicking on that DCIM folder?

Same problem here, cannot import anything from the SD card on an iMac.

And Adobe support is like "Meh, you're using Catalina, not compatible". At least at got a shot at starting a trial of Capture 1, which is actually pretty good... and can read a SD card.

Thank you I will try this tonight!

Go to the finder and look at that destinations folder. Does it have a pencil with a line through it in the lower left-hand corner of the window? That means you can’t write to that folder, as the error message states. Try Get Info on that folder, then go down to where you see your username and the other “users”, and check to see if you have read/write permissions. If not click on your username, unlock the lock, and give yourself those permissions.

Question. Are you all able to edit the photos or just preview? Because I am able to preview doing the things you suggested but the RAW files will still not import. I get an error screen (see image).

On the issue for SD cards, In Source, Devices vs Files. See “Lightroom Classic Only Updates”
in: https://lightroomkillertips.com/may-2019-update-for-lightroom-classic-lightroom-and-adobe-camera-raw/ 

If you select it from the Files section of the dialog, as you have in your screenshot above, then you can preview them fine (and in my experience, it's the faster import too). It's only an issue when accessing the card as a "device" instead.

Does it mean you also cannot directly preview anything from your SD card when inserted into the MacBook after installing Catalina? I hope Adobe resolves this issue soon, as going round and round eventually being able to preview the unimported files is not really the solution. 

I've updated my laptop to Catalina and verified this issue. Thanks for reporting it, I'll file a full bug report.