Thank you very much.
My retailer does not answer, very disappointing. So I cannot tell why they used FFS.
Yes, I use AmigaOS 4 as well as MorphOS on my X5000 but they are installed on two different SSDs. And I never have both connected, always only one.

So, if I understand it right, I should format the system partition with SFS, before I reinstall MorphOS.

Can you/someone please tell me in a detailed way: How?
And after that, I reboot via USB stick and start installation?