Can't boot into or mount Mojave APFS partition after repartitioning for Linux MacBook Pro 2015, 256GB SSD disk
I have created a second partition on my disk to try Linux. Everything was fine, but at some point, macOS disappeared from the boot menu.
After some googling and trying some things, I thought it was a problem with the boot manager. I installed rEFInd but it didn't help. So I tried torecover everything using recovery mode. But there was no option to reinstall macOS on the first partition. I could only erase it. I also couldn't mount it to macOS Recovery.
I installed OS X 10.10 Yosemite (base for my MacBook) on the second partition and updated it to macOS 10.14 Mojave (to be able to mount that first APFS partition). But I still can't mount it:
daniils-MacBook-Pro:Volumes daniilkk_yose$ sudo mount -t apfs /dev/disk0s2 plz/
mount_apfs: mount: Inappropriate file type or format

Also, diskutil outputs many F's instead of type and name:
daniils-MacBook-Pro:Volumes daniilkk_yose$ diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *251.0 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2: FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF               129.2 GB   disk0s2
   3:                 Apple_APFS Container disk1         121.6 GB   disk0s3

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +121.6 GB   disk1
                                 Physical Store disk0s3
   1:                APFS Volume disk1s3                 12.8 GB    disk1s1
   2:                APFS Volume Preboot                 43.1 MB    disk1s2
   3:                APFS Volume Recovery                510.4 MB   disk1s3
   4:                APFS Volume VM                      1.1 GB     disk1s4

Disk Utility doesn't show this partition at all:

Is there a way to mount it and get my data back?
I've had exactly the same issue on an older MBP running 10.13.6.  I've tried twice to work around it and got your problem.
In the end (both times) I had to do a recovery using internet recovery (option-command-r) and then restore my stuff from Time Machine.
I looked at rEFInd but didn't install it, so I can't say how to drive it.
It seems that APFS doesn't like to be messed with.  I'm looking at dropping the APFS and just living with the old journaled FS as a fixed size partition.
After that, I figure I can tinker with the EFI partition until I get it right.