A few years ago, I spent a fair share of time trying to copy files from and to a Macintosh Plus. I decided to use a 100 MB ZIP drive (actually two of them, SCSI for the Mac Plus and USB for a modern computer) and later a serial port connection with terminal software [1].
Now there's a much better and cheaper option: BlueSCSI [2]. It's a SCSI HDD emulator that allows to mount .img files stored on a SD card as HDD disks. It also supports CD and network card emulation.
Once the files are copied on a such a virtual drive, they can be extracted on a modern machine using via some kind of HFS explorer or an emulator.
They were proprietary and made by only one company. So there was a bit of a battle between Zip, SyQuest and LS120 ("SuperDisk")
What I don't get is why Magneto-Optical didn't take off. 3.5" disks that were essentially MiniDisc but not proprietary (there were drives and disks from several manufacturers), faster than Zip, and eventually got upgraded to over 1 GB capacity disks. They were huge in Japan where they became a de-facto standard, but mostly unheard of in the rest of the world.
They sorta did in the Apple world. Maybe not quite a standard, but quite common. Apple shipped several Macs with (optionally) built-in Zip drives in the late 1990s.
Now there's a much better and cheaper option: BlueSCSI [2]. It's a SCSI HDD emulator that allows to mount .img files stored on a SD card as HDD disks. It also supports CD and network card emulation.
Once the files are copied on a such a virtual drive, they can be extracted on a modern machine using via some kind of HFS explorer or an emulator.
[1] https://blog.rekawek.eu/2016/12/08/mac-plus#hard-drive
[2] https://bluescsi.com/