Why doesn't my external hard drive work with Catalina?
I just bought a new Mac Mini with OS Catalina on it and my 10 year old Buffalo 2.0 brand external hard drive won't work with it. It would work with OS Mojave. My 2018 vintage Seagate external hard drive works with Catalina.
Overall, I haven't been impressed by Catalina. Hopefully Apple will have upgrade fixes soon regarding to Catalina's bugs.