I built and installed the zfs-dkms-git-2019.09.27.r5421.g7bb0c2946-1 package from AUR this mourning with out any issues.
Assuming you installed the linux-rpi4-headers package I noticed that there was not any depends in the AUR zfs-dkms package PKGBUILD declared. The one package that stuck out to me was lsb-release that was in the zfs-dkms-git package PKGBUILD as a depend not to mention zfs-utils-git was not there as well.
Here is my built packages and their modified PKGBUILDS that reflects the aarch64 architecture.
Upgrade your kernel and it's headers to the latest if you have not done so to 4.19.75-1-MANJARO-ARM:
Install zfs-utils-git-2019.09.27.r5421.g7bb0c2946-1-aarch64.pkg.tar.xz first
Be advised that it took 15 1/2 minutes here to install the zfs-dkms-git package.
It will also take the same 15 minutes after a kernel upgrade on reboot while DKMS rebuilds the modules.
(2/2) Install DKMS modules
==> dkms install zfs/git -k 4.19.75-1-MANJARO-ARM