Did you run manjaro while both ssd`s where inside ?
It’s forbidden for btrfs to use a clone while the original is reachable from the kernel! (says the btrfs-wiki)
This will in most cases result in severe damage to both btrfs filesystems.
I must know, because i destroyed an install of manjaro this way.
This may happen, because the kernel does select btrfs filesystems by UUID (which is the same for both). And when finding 2 btrfs-filesystems with the same UUID, the kernel gets confused, because this seems to be a indicator that these belong to a btrfs RAID !
No, as I wrote the original ssd is removed, I have guessed that this would be problematic Maybe I need to edit the boot/grub? The old disk was sdb the new is sda. No idea how, my linux knowledge is still limited. I did a lot of searching, seems that cloning disks ws ith btrfs is not an easy thing. But I dont give up yet, there must be a simple solution.