Thanks P.Philips
first try:
I type unmount WD B the disk flashes a few times, then the little lamp stays on. However, the disc logo remains on the screen.
After three minutes the lamp flashes a few times and comes back on without flashing. The disc logo is still on my screen.
So I dare not remove the disc.
What to do ?
I open Disk Utility and ask for an SOS on the external drive. The disc logo is still on my screen! I drag it to the trash, the logo disappears from my screen.
Then I look again at disk utility. AND the external drive is still in the disk utility! while it is no longer on my screen!
After a few minutes this is what happens;
1. The logo is no longer on my screen
2.the small lamp flashes slowly
3.I put my hand on the disc and do not feel any movement in it
4.I open utility disk the mother disk is still present
but the WD B segment has turned gray (so like an ejected part)
second trial
As I do not feel anything spinning in the external disk, I remove the plug knowing that the lamp flashes. The MBP is not showing me an eject error.
I reconnect the external drive. I open Disk utility and notice that the mother drive and the WD B segment are present.
I ask for an SOS, then in disk utility click on eject. I put my hand on the disk and don't feel any movement,
but the lamp flashes slowly. I remove the cable and get no error message.
This second try looks good, but I don't like it at all since I removed the cable while the lamp flashes.
So the problem is not resolved. I wonder if I won't go back to Mojave and wait better times.
PS the Drive Genius 6 app does not work either.
NordVPN was also not working. I have already lost days of work.
Thank you all for your good will.