poor read speeds from USB thumb drive

Hi all,

I just received my 2021 16-inch MacBook Pro to replace my dead 2013 model. I use a 128 GB thumb drive formatted with exfat fs. This worked fine on my old Mac. When I plug in the drive using a USB-C to USB-3 dongle the read performance is abysmal, in the KB/s range.

Any ideas? I was thinking about reformatting the drive but that would mean losing everything on the drive, and I cannot copy the files off of it due to the performance.

Thanks for your help.