Now I decided to set up an Outlook e-mail account. What happened? Nothing! All working as expected by automatic setup without any manual changes. I never imagined that a Microsoft product was a solution. I was not using this account and in fact it was only created for digital licence I have of W10. Now it seems I will have to redirect may GMail emails to Outlook if I want to use Thunderbird...
TROUBLESHOOTING INFORMATION SCREEN
Application Basics
Name: Thunderbird
Version: 45.8.0
User Agent: Mozilla/5.0 (OS/2; Warp 4.5; rv:45.0) Gecko/20100101 Thunderbird/45.8.0
Profile Directory: Open Directory
(Unknown location)
Application Build ID: 20200322201630
Enabled Plugins: about:plugins
Build Configuration: about:buildconfig
Memory Use: about:memory
Mail and News Accounts
account1:
INCOMING: account1, , (imap) outlook.office365.com:993, SSL, passwordCleartext
OUTGOING: , smtp.office365.com:587, alwaysSTARTTLS, passwordCleartext, true