Yes, that’s right: mlocate is dead. Long live plocate! 
plocate is a drop-in replacement for mlocate, except the service files are named differently. That is the cause of this error:
The new service file is called plocate-updatedb.service.
I just pushed through a commit for the garuda-update script to address this:
The new version is already in the repo (garuda-update 4.8.1-1); if you run the update again you should be able to pull it down if your mirror is up to date.
The only “gotcha” is our existing /etc/updatedb.conf file is being saved as a pacsave.
The new file it is being replaced with is exactly the same, except it is missing a consideration that was added for excluding snapshots when building the database used by plocate (formerly mlocate).
PRUNE_BIND_MOUNTS = "yes"
PRUNEFS = "9p afs anon_inodefs auto autofs bdev binfmt_misc cgroup cifs coda configfs cpuset cramfs debugfs devpts devtmpfs ecryptfs exofs ftpfs fuse fuse.encfs fuse.s3fs fuse.sshfs fusectl gfs gfs2 hugetlbfs inotifyfs iso9660 jffs2 lustre mqueue ncpfs nfs nfs4 nfsd pipefs proc ramfs rootfs rpc_pipefs securityfs selinuxfs sfs shfs smbfs sockfs sshfs sysfs tmpfs ubifs udf usbfs vboxsf"
PRUNENAMES = ".git .hg .svn"
# Modified by Garuda Linux to exclude snapshots
PRUNEPATHS = "/afs /media /mnt /net /sfs /tmp /udev /var/cache /var/lib/pacman/local /var/lock /var/run /var/spool /var/tmp /.snapshots"
Aside from the commented line, the only difference between the two files is the addition of /.snapshots to the PRUNEPATHS line.
In this case, the pacsave (the original file) should be kept, overwriting the new version.
sudo mv /etc/updatedb.conf.pacsave /etc/updatedb.conf
@TNE @dr460nf1r3 maybe this last piece could be added as a hotfix.