Catalina and external hard drives
Since I found a solution for my problem this is more like a confirmation of what I read about Catalina. I have the issue with two HDD (Toshiba 2GB and WD 5GB) not being mounted by my MBP 2017 running Catalina. The smaller drive was at least shown several times as unrepairable but still accessible to copy data where the bigger one never mounted.
My solution: The "broken" drives work properly without any complaints on my old Mac Mini 2010 running High Sierra.
But I have a question after all: When will it be save to connect the drives to the MBP again?
MacBook Pro 15″, macOS 10.15