UPDATE3: I have finally figured out how to fix this issue!
First, I removed the Norton 360 app from the Applications folder and proceeded the removal process.
Second, I used the removal tool for mac from here:
https://support.norton.com/sp/en/us/home/current/solutions/kb20080427024142EN
After that, I ran the searching command on my mac in the terminal app to find some remaining files & folders that contain "norton" or "symantec" in their file paths:
$ sudo find / -name *norton*
and
$ sudo find / -name *symantec*
Even after applying the removal tool mentioned above there were several dozens of such files & folders. So, at my own risk, I decided to remove all those files & folders and that did the trick!
I am not sure what files & folders are responsible for the issue I had but, I suppose, those are the ones that are responsible for WebKit cookies and cache. For example, files such as following (where "roman" is a mac user name):
/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_ru.norton.com_0.localstorage-wal
/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_ru.norton.com_0.localstorage-shm
/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_login.norton.com_0.localstorage-wal
/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_login.norton.com_0.localstorage-shm
/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_login.norton.com_0.localstorage
/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_ru.norton.com_0.localstorage
/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_support.norton.com_0.localstorage-shm
/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_support.norton.com_0.localstorage
/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_support.norton.com_0.localstorage-wal
and:
/System/Volumes/Data/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_ru.norton.com_0.localstorage-wal
/System/Volumes/Data/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_ru.norton.com_0.localstorage-shm
/System/Volumes/Data/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_login.norton.com_0.localstorage-wal
/System/Volumes/Data/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_login.norton.com_0.localstorage-shm
/System/Volumes/Data/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_login.norton.com_0.localstorage
/System/Volumes/Data/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_ru.norton.com_0.localstorage
/System/Volumes/Data/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_support.norton.com_0.localstorage-shm
/System/Volumes/Data/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_support.norton.com_0.localstorage
/System/Volumes/Data/Users/roman/Library/WebKit/com.symantec.mes/WebsiteData/LocalStorage/https_support.norton.com_0.localstorage-wal
Also I found files such as:
/System/Volumes/Data/private/var/root/Library/Cookies/com.symantec.daemon.binarycookies_tmp_129_0.dat
/System/Volumes/Data/private/var/db/com.symantec
/System/Volumes/Data/Users/roman/Library/HTTPStorages/com.symantec.mes.binarycookies
So, I think, the developers of the removal tool should add those extra files & folders to the removal list.
DISCLAIMER & ATTENTION:
I USED THE COMMAND sudo rm -rf AT MY OWN RISK! USING THIS COMMAND CARELESSLY CAN REMOVE OR DESTROY SOME OF YOUR DATA!
To remove a folder from the terminal app I used the command "sudo rm -rf path/to/the/folder" where you can substitute required folder path such as "/System/Volumes/Data/Users/roman/Library/WebKit/com.symantec.mes" instead of "path/to/the/folder".
Break down of the "sudo rm -rf path/to/the/folder" command:
- sudo - run the following command as an administrator
- rm - remove
- -rf - recursively (for folders) and forced (not asking for confirmation)
- path/to/the/folder - a placeholder, use a real path here to remove
FINALLY
I reinstalled the Norton 360 application, and I was able to sign in and activate the app.