If you are struggling to read SDXC cards in your card reader in Linux, specifically Ubuntu (I'm on 20.04), this is because the Realtek SD card reader driver is broken in the standard 5.4 kernel. It is possible to manually edit the driver and recompile the kernel, but this may be overkill for most users.
To get a working driver, install the newest kernel for better hardware support:
sudo apt install linux-generic-hwe
And then reboot your laptop.
The kernel bug report is found here