From what I've just discovered using two different M1 Macs, don't use USB mode with this processor. It will see the files, but copying them stalls and partially copies them. I was worred that the SSD was corrupted or something, but I flicked the USB mode off and it was back to normal.
Edit: See below, some users on Windows are also experiencing similar issues

I have exactly the same problem. Very slow and faltering transmission with USB mode. Without mode normal relatively fast transmission. Windows - AMD Ryzen 9 5950X - X570 Aorus pro. But it won't be because of the PC, because my old PC Intel core I7 2600 shows exactly the same. Can I have done something wrong? What are your experiences. Does this work for you?

Hello there CloudVisual. Thank you for reaching out and for sharing these information with us. Again, thank you for your support and have a nice day.

Interesting. FWIW, no problems with USB mode on an Intel mac. It works great and I love it- no more distracting LEDs flashing. Such an improvement!

Hi seattle_helo. can you tell me the order of how you did it. Is it the same in USB mode? How exactly do you do it? maybe I have a mistake there. When I'm in USB mode, I can't eject the SSD anymore either. In normal mode, this works quite normally and well.

Tried it on a 2nd Mavic 3 cine today. It worked here. There was no additional SD card inserted in this Mavic 3. That was the reason. As soon as I removed the SD card from the 1st Mavic 3 cine, it also worked with the 1st Mavic. That was the reason. The additional SD card (reserve memory) would be important to me. It would be nice if DJI changed that.

As I reported today (1/27) on a different thread, USB mode worked fine on multiple Macs running Monterey 12.1.  When I updated to 12.2 today, USB mode failed to function. The M3C's internal SSD mounted and showed files, but downloading them was all but impossible.  The SSD could not be ejected.  Activity Monitor showed that the Finder was non-responsive.

Are you running Monterey 12.2 or an earlier OS version?

I'm running Big Sur v11.6.2. I usually hold back on the OS to help ensure nothing breaks my post workflow.

I connect the drone (M3C) to the mac via the included lightspeed data cable. Then I power the drone on. It goes thru the startup routine and initialization but right after the IMU checks the SD_Card and SDD mount to the desktop and then the LEDs go dark and the drone enters USB mode. No problems reading or transferring data from the SSD.   

I have noticed however that the SSD will not eject properly when the SD card is inserted. With the mSD card removed you can eject the SSD properly/instantly as normal. I think I read in the release notes the USB mode is not compatible with the mSD card. Kind of an interesting limitation.

Okay, yes, just found it again in the updated user manual (v1.4) :

It's worth me saying that USB Mode is only required if your PC/Laptop has a slow HDD. If you use the supplied USB-C cable and are offloading to a good spec SSD, you can offload an entire M3 1TB SSD in about 30 minutes.