After a lot of help here from the forum, the only two open items, I will bring up only one item here:

Installed Windows 10 Guest, it seems all works well, and the only outstanding is - I can't see my External WD backup hard disk while in File Manager in the Windows Guest.

I can see any USB stick that is connected, but NOT that har disk

Thanks

What type of port is it plugged into, USB 1,2 or 3?

I believe you installed Guest Additions for Widows but did you enable USB 2 or 3 support in the Windows virtual machine settings? To change settings you need to shutdown the VM.

If you look at the VM devices pull down menu does the drive show in the list of USB devices? If so you need to select it and "attach" it to the VM if not already so. There should be a checkmark on the left side. If that all has been verified then the drive should be automatically recognized in Windows if it is formatted as NTFS, exFAT or FAT32.

I didn't see an option to set type of USB 3, but in the setup of the Guest Devices, it shows that USB 3 is selected.
I tried plugging the external drive into ALL the 4 USB ports on my laptop, but neither shows the drive in File Manager.

When people say VM, is it related to the HOST or the GUEST?

Yes, in Devices->USB the drive shows in the drop down, I check the box but it still doesn't show up in File Manager
Now, what can be the problem, the drive is formatted as ext4, not any of the other options you mention. Once I plug-in an ExFAT formatted drive, it shows up in the File Manager.

Many thanks again, I will mark it as SOLVED

Cheers

By VM I mean the guest. Windows does not natively have the capability to read linux filesystems.

Thanks again for your help along the way.
My next, install macos VM