My 2015 iMac running Mojave sees SSD drives formatted with APFS but won't allow me to access any of the files on them. When I tried utilizing the drive in Recovery mode, I couldn't modify either drive in any way. What gives? My newest drive had to be formatted in Mac OS Extended Journal just to get up and running again.
iMac 27″, macOS 10.14
Mojave's APFS was I believe offered as an early beta, if not the earliest production implementation of the APFS spec, and Apple has augmented APFS functionality in subsequent operating system releases. You do not specifically state what operating system was used to format your "newest" drive as APFS, and that may be a contributing factor in the backwards compatibility story. So might the solid state drive vendor, model, and external enclosure type.
I have no Samsung drives here to test, as I am exclusively Crucial. I noticed the Samsung Magician page and a Mac firmware update for the 870 EVO, but Samsung does not give a creation date for that 29MB Mac specific firmware .iso download. As with any drive firmware update, caveat emptor about it potentially wiping the drive data. Your drive issues may or may not be firmware related, but there are years of Samsung drive issues posted in these communities, so perhaps.
APFS was listed as useable on anything after Sierra on all of sites I looked at. https://www.seagate.com/support/kb/how-to-format-your-drive-apfs-on-macos-high-sierra-to-catalina/ Both my original fusion drive and the new drive replacing it are using Mojave. You're right, I didn't list what it was using on the new one.
My original fusion drive was failing so I had a computer repairman recover the data. He placed it on an external Toshiba utilizing the APFS format. When I realized my machine couldn't utilize it, I bought another drive. This second SSD was an internal Samsung 870 EVO which was running in a standard run of the mill case utilizing USB3. When I installed APFS on that blank drive (via a functioning mac), my machine wouldn't allow me to install the OS, it was not available for use when selecting a drive on a system boot in Recover mode. I could see it in disk utility but I could make no changes to it. Once I got it working with Mac OS Extended Journal, it replaced the dying fusion drive inside my iMac. Now I'm trying to see if I can access the recovered footage on the external Toshiba drive but it shows up as empty. I know it's not because Disk Utility shows half the space it has is being used by my recovered data.
The reason I simply don't update to a later OS is because Apple drop support for 32 bit application after Mojave and I occasionally still utilize a few. 32-bit app compatibility with macOS High Sierra 10.13.4 and later - Apple Support
APFS can be seen by OS but not read.
