I also have the exact same situation. I was almost trying to downgrade my MBP16', but I changed my mind after reading your post. Thanks a lot..... My SSD and HD are ExFAT formatted. It works in Catalina and Windows perfectly.....
atomuto
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I have same problems with new MacBook pro 16'. No HDD nor SSD. They worked totally fine with old MB pro 13' with Catalina.