How to create new btrfs partition on attached harddrive and make snapper create snapshot for them?

Hello Garuda users.
I want to
Either
make snapper create snapshot of /dev/sda1 partition on a .snapshot folder like it does for root filesystem
OR
mount subvolume '@' present on /dev/sda1 to /mnt/rom , because timeshift only backups @ subvolume and currently all my data is in /mnt/hdd in open not inside any subvolume

ls -la /mnt/hdd

drwx------    - user    23 Aug 17:21  .
drwxr-xr-x    - root 13 Aug 20:16  ..
drwxr-xr-x    - root 23 Aug 17:20  @
drwxr-xr-x    - root 23 Aug 17:21  timeshift-btrfs

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