Solved BIOS detects at new HDD failure 6 - what to do?

SMART attribute 6 records data relevant to Read Channel Margin and is not an attribute commonly included in failure prediction. WD does not track - and does not store and does not report - this value.

SMART data as a whole is stored on the HDD controller board and does not care if your HDD is formatted for Linux, Apple, Intel, et cetera. SMART data relates to hardware. Disk formats etc are software.

The 6 refers to SATA port 6.
Run any SMART tool to read the SMART report to identify the specific failing SMART attribute(s).
https://crystalmark.info/software/CrystalDiskInfo/index-e.html

Buy a new hard drive.

There are tricks available that will allow you to bypass this catastrophic error.

Such trickery will, without exception, delay a subsequent catastrophic failure at some random point in the immediate term.

You could use GParted Live to isolate the lead portion of the disk and forcibly move the boot sector to another area on the disk. Under some circumstances and some trial and error, you could create partitions "around" the flawed portion of this disk platter. But this is pointless and an exercise valid only for proof of concept.

Your disk has failed due to physical damage - either to a platter or the armature or the read head. If it is the read head, all efforts to bypass the catastrophic failure are pointless. If it is the armature, all efforts to bypass the catastrophic failure are pointless. If it is the platter - and there is no corresponding or related damage to the armature or the read head - the internal environment of the disk assembly is compromised.

All that being said - you could purchase a copy of SpinRite. The purchase price exceeds the cost of a new disk - and probably will not work. SpinRite is best used to recover data from a disk, not force a catastrophic failure to work for a worthwhile period of time.

https://www.grc.com/cs/prepurch.htm

That sounds like you tried SpinRite. Please confirm.

And to make the point as clearly as I can -
SpinRite is a data recovery tool. SpinRite repairs are a temporary solution. SpinRite will not repair the physical damage on the disk. The disk will fail again and when it does, there will be a drastic reduction in the likelihood that SpinRite can perform a second recovery.

The difference being that on the first SMART failure, no data was in jeopardy. On the next failure, all data is subject to loss.

Buy a new hard drive.

I marked the thread as Solved for you.