@fg2001
I use Windows 10 Pro - Version 1909 - OS build: 18363.959 and this Windows Defender problem also occurs on my PC.
Jose,
The quick removal for external drives is already set as default. That is not the issue, when eject is issued they should first stop the activity of windows defender on the drive and then eject correctly.
If you see the problem also with 1909, that means that they introduced the bug with some recent changes of the defender also in 1909.
I had 1909 for over a year and never had any problems with eject.
It all started for me with v 2004 in 5 different machines.
Also I don't get the problem with any insider development build up to build 20180.