Create an APFS RAM disk
It works if you create a JHFS+ volume first and convert it to APFS in a second step:


DISK_ID=$(hdiutil attach -nomount ram://$((&lt;number_of_blocks&gt;)))
diskutil eraseDisk JHFS+ "RAM Disk" $DISK_ID
diskutil apfs convert $(tr -d ' '&lt;&lt;&lt;${DISK_ID}s2)


If the RAM disk has a size of 2 GiB (4 * 1024 * 1024)(block_size) or smaller no EFI partition is created and the 3rd command is: diskutil apfs convert $(tr -d ' '&lt;&lt;&lt;${DISK_ID}s1) or more generally:

DISK_ID=$(hdiutil attach -nomount ram://$((&lt;number_of_blocks&gt;)))
SIZE=$(diskutil info $DISK_ID | awk -F'[^0-9]*' '/Disk Size/ {print$4}')
diskutil eraseDisk JHFS+ "RAM Disk" $DISK_ID
if [ $SIZE -le 2147483648 ]; then diskutil apfs convert $(tr -d ' '&lt;&lt;&lt;${DISK_ID}s1); else diskutil apfs convert $(tr -d ' '&lt;&lt;&lt;${DISK_ID}s2); fi


Result:

...
/dev/disk2 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        +4.3 GB     disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                 Apple_APFS Container disk3         4.0 GB     disk2s2

/dev/disk3 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +4.0 GB     disk3
                                 Physical Store disk2s2
   1:                APFS Volume RAM Disk                32.8 KB    disk3s1