Create xfs partitions on Hetzner via cloud-init. It keeps root disk available again after rebooting. Simply change your desired sizes and filesystem to use it for your needs.

xfs-on-hetzner.yml

#cloud-config
resize_rootfs: false

disk_setup:
  /dev/sda:
    table_type: 'mbr'
    layout:
      - 25
      - 75
    overwrite: true

fs_setup:
  - label: root_fs
    filesystem: 'ext4'
    device: /dev/sda
    partition: sda1
    overwrite: true
  - label: data_disk
    filesystem: 'xfs'
    device: /dev/sda
    partition: sda2
    overwrite: true

runcmd:
  - [ partx, --update, /dev/sda ]
  - [ mkfs.xfs, /dev/sda2 ]
  - [ partprobe ]
  - parted /dev/sda set 1 boot on p

mounts:
  - ["/dev/sda1", "/"]
  - ["/dev/sda2", "/data_disk"]