On inserting exfat-formatted SD card with USB adapter mounting via KDE UI results in these options:
sudo mount | rg -i sdb
/dev/sdb1 on /run/media/user/9C33-6BBD type fuseblk (rw,nosuid,nodev,relatime,user_id=0,group_id=0,default_permissions,allow_other,blksize=4096,uhelper=udisks2)
Average copy (with Dolphin, 80GB ~3000 files) speed is about 10 Mb/s.
If I insert the card into Android device (DAP), and connect the device with USB to the workstation, I get ~2x faster copying.
So, my guess is I need to use some another/additional mounting options to get at least the same speed.
Well, there’s more than just the USB connection at play here. The card reader itself also has to be able to handle the throughput, and then it also matters what USB port on the computer you use. Many computers today are equipped with both USB 2.x and USB 3.x ports — the latter usually have a blue plastic insert to distinguish them from USB 2.x ports.
Here’s what Wonkypedia has to say about it.
So it would appear that either your reader or the USB port on the computer is USB 1.x, but I doubt whether that would be the case for the computer itself. Therefore, my money would be on the reader being the bottleneck.