“First Aid process has Failed. If possible back up the data on this volume.” Error on my MacBook Pro

Try running First Aid in Restore Mode...

Start up from macOS Recovery

Option-⌘-R

Upgrade to the latest macOS compatible with your Mac.

In Disk Utility>View, select Show all Devices, highlight the top left entry.

Run Disk First Aid on all items in the left panel, from top down.

What OS version & what Format is the drive?

Wllwlwlwlwlwlw wrote:

I used to get yellow warnings a lot but they were fixed, i used an unsupported OS so APFS does not work properly and is not able to repair it in this HD but in others, it gives me a yellow warning and fixes it and done.

If we correctly understand the above statement ?

That, is Not Supported by Apple

The issues presented maybe directly related to using unsupported methods to run that version of macOS on this computer

Sometimes it is necessary to rerun First Aid multiple times to get an ok result.