from the developer
As this was not tied to any version, it should work for everyone now.
Hi all,I would like to share some news 
This morning Google has approved our verification request to allow KMail/Kontact to sign into Gmail using the Google Sign In, which supports 2FA out-of-the-box and is more secure, since KMail/Kontact never sees your password.
If you have your IMAP account in KMail already configured in KMail and you would like to start using the OAuth sign-in, go to the account configuration (Settings→Configure KMail→Accounts→Receiving→[your Gmail IMAP account]→Modify) and in the Advanced tab select "Gmail" in the Authentication combo box.
If you want to add a new account, the Gmail authentication method will be chosen automatically by KMail.
I apologize it took so long to make Gmail login work again. The bureaucracy that had to be sorted out in order to comply with Google usage policies was non-trivial and I'll admit then whenever I had some spare time to work on KDE, I usually chose to write some code rather than read legal documents and write privacy policy...
Should you still see "Sign in with Google temporarily disabled for this app" or some other error, let me know, please.
This morning Google has approved our verification request to allow KMail/Kontact to sign into Gmail using the Google Sign In, which supports 2FA out-of-the-box and is more secure, since KMail/Kontact never sees your password.If you have your IMAP account in KMail already configured in KMail and you would like to start using the OAuth sign-in, go to the account configuration (Settings→Configure KMail→Accounts→Receiving→[your Gmail IMAP account]→Modify) and in the Advanced tab select "Gmail" in the Authentication combo box.
If you want to add a new account, the Gmail authentication method will be chosen automatically by KMail.
I apologize it took so long to make Gmail login work again. The bureaucracy that had to be sorted out in order to comply with Google usage policies was non-trivial and I'll admit then whenever I had some spare time to work on KDE, I usually chose to write some code rather than read legal documents and write privacy policy...
Should you still see "Sign in with Google temporarily disabled for this app" or some other error, let me know, please.