I dont understand why you open 2 Topics for the same problem, you just splitt the information.
The OP seems to have no understanding of the problem. While this isn’t uncommon for inexperienced computer users, they might legitimately think that the new thread relates to another issue entirely.
This is not the case.
The problem is that the OP is trying to boot both BIOS/MBR and UEFI. This is obvious simply by looking at their provided system information.
You can not boot a MBR booting OS and a UEFI booting OS at the same time. This is why, if you disconnect one disk, the other disk will still boot as expected.
IT IS THE SAME PROBLEM I DESCRIBED ABOVE
[Capitals used to enhance your understanding.]
This second thread is unnecessary:
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Discussion continues in new topic - Manjaro not starting XFCE when windows drive is connected via SATA