I have a SSD Powered On, that i don’t use in Linux anyways, because this SSD is for Windows10/Windows Games only and its actually just power waste.
I want to shutdown my unused Internal drive: /dev/sda
Is there a easy command for this?
I know for a External USB Drive i would normaly use:
udisksctl power-off -b /dev/sda
But thats not gonna work for a Internal Drive 
Instead of shutting it down why not place an entry in /etc/fstab; or use gnome-disk-utility; to prevent it from mounting automatically. You can always mount and unmount it manually, if ever needed from Manjaro.
If not mounted, wear and tear on an SSD is virtually non-existent.
I also use this premise to prevent Windows from offering to format an empty – but not really empty, Linux partition.
I think this is only possible via (not recommended) hardware methods:
Its not mounted in fstab… it never was.
Thats no solution for me
It’s not mounting at all?
That being the case, all I can suggest is to buy yourself a removable caddy (not USB) and keep the disk in that; push the button to eject it any time you want.
Something like this, for example.
gnome-disk-utility (Disks) also allows you to hide disks / partitions from your File Manager, if that is all you need to happen.
Its hidden in dolphin already, but thanks for trying to help me. 
Just sad, i can’t shutdown this Drive with a simple command
Would not this work?
sudo hdparm -Y /dev/sda
Or … maybe better … to use UUID… after finding with blkid
sudo hdparm -Y /dev/disk/by-uuid/THE-UUID-OF-THE-DEVICE
complementary wiki link:
https://wiki.archlinux.org/title/Hdparm#Power_off_a_hard_disk_drive
better:
sudo hdparm -y /dev/sda
Case often matters.
Nah no changes…
/dev/sda:
issuing sleep command
They still shown in dolphin. 