I haven’t updated to Mojave yet but I need to do. I recently updated to the latest High Sierra and my Seagate external backup drive no longer works. Seagate acknowledges it.
I’m considering buying the new MacBook Air this weekend. I have to decide on what storage size I’ll need but if I want an external backup drive I have no idea what will work now with Mojave. Kinda frustrating especially because I can’t use my current Seagate to restore to a new computer.
I’m still using the 2011 edition (updated many times) of the iMac desk top...
I haven't updated to Mojave either. But when I do, I will have cloned both my internal storage and external storage before updating. That gives you the ability to boot either from the newly updated OS, or you can boot from the clone on an external HD in order to access the former OS version. Every time I update the OS, I clone and keep the former version. Saves grief in case existing applications or peripherals don't work on the new OS. (Really saved me when old stuff had problems with a new OS.)