After hitting <Option>+<e> the keyboard layout changes to Greek although Greek is not listed as Input Source

Hi,

I have a MacBook Pro (15-inch, Mid 2012), processor 2.6GHz Quad-Core Intel Core i7. I always run the latest of the MacOS and it is today 10.15.7. /Today is Oct 30, 2020./ To use accented letters, I frequently used <Option>+<e> and <Option>+<u> key combinations in the past. About two weeks ago, after an update from Apple, as soon as I hit <Option>+<e> the keyboard layout has changed to Greek, although I have not had Greek as an Input Source.

Interestingly the first item under the Apple logo menu was "System Information", that is the "About This Mac" item disappeared. Also in the applications, for example in Safari, the "Quit" item was changed to "Quit and keep Windows". Notable also that by <control>+ click on a file does NOT bring up the popup to open the file.

First I thought it was a Facebook error, because I was using Facebook Messenger in Safari, but after reinstalling the OS, I could cause it in FireFox and Google Chrome without Facebook, so I think it is an OS problem.

First I could not log in, because not just my user keyboard layout was changed, but also the System keyboard layout too. In System Preferences in Keyboard I have just U.S. English as input source, nothing else.

Fortunately after 5-6 reboot I was able to login, but as soon as I logged in, the keyboard layout was changed to Greek again. In the meantime I changed from WIFI to wired Ethernet and after some reboots again where I tried <Shift>, than <Option>, the machine ignored all and of course I could not boot from a CD either because the <c> key was not a "c" anymore. So, playing it for a few days and being away from home, I could not do anything on my MacBook Pro. After arriving home on Oct 27 I had some lovely chats twice with Apple Support who were clueless about this particular problem, but they set me up to see a techie in an Apple Store tomorrow. After some research I found an article which recommended to trash the following two files from my machine: /The second file for you might be different, because I do not have my home directory on the boot volume/

/Library/Preferences/com.apple.HIToolbox.plist

/Volume/Other/janos/Library/Preferences/com.apple.HIToolbox.plist

I was able to do so, because after some trial booting into Recovery mode again, the machine really booted into Recovery mode, so I could delete the files and not just delete them but also reformat my boot drive and reinstall Catalina fresh. Before doing that I deleted the

/Library/Preferences/com.apple.HIToolbox.plist

from the recovery volume too, just to be sure.

After the reinstall I was able to login and do a few things, but as soon as I tried again using the <Option>+<e> key combo, the keyboard layout went Greek again. There are here two possibilities:

1. Somehow this Greek keyboard layout - which is NOT listed as an Input source -, survives a fresh OS install, which sounds unbelievable.
2. This <Option>+<e> key combo is built into the OS to change the keyboard layout to Greek and this is also unbelievable,.....but for me has a higher probability than the previous point 1.

Now, if I accidentally hit <Option>+<e> or <Option>+<u> my workaround is, to reboot into Recovery mode - if I can - and delete the two HIToolbox.plist files, which is very cumbersome.

I am all ears for a final solution to this problem.

Thanks ahead,

Janos