backup dir 

Define a backup dir:

BACKUP_DIR="/opt/backup/backup-$(date +%Y-%m-%d_%H-%M)"

Take the backup: 

mariabackup --backup --parallel=2 --safe-slave-backup --target-dir="$BACKUP_DIR"

prepare 

Not required but nice to have since you can save work and ensure backup can be restored without any problems and faster

mariabackup --prepare --target-dir="$BACKUP_DIR"

compress 

tar -cf -"${BACKUP_DIR##*/}" | zstd > "$BACKUP_DIR.tar.zst"