Hi all
I have the same problem with my 256GB Lexar card and Catalina, but I found a (bit unconventional) solution.
I installed home-brew (OS X Packagemanager) and gave Midnight-Commander a chance.. and it worked fine.
So install home-brew in Terminal (infos on hombres website, it's easy going) - install Midnight-Commander (brew install mc) - launch mc and copy your card... voila!
It's not the fine english art of copying files but it works ;-)
greetings Tom