Yesterday, I've discovered that KMail (5.7.3) on my Kubuntu 18.04 doesn't synchronize with Google mail inbox. I tried to re-create the gmail account, but after logging into Google I received the following message:
Sign in with Google temporarily disabled for this app
This app has not been verified yet by Google in order to use Google Sign In.
Is that global problem that KMail stopped working with Google or just mine? Is it possible to solve/workaround it? Maybe it's possible to bypass KMail wizard and log into Google account using an app password?
I've been observing the KDE bug regarding this: https://bugs.kde.org/show_bug.cgi?id=404990. To summarize discussions in the bug's comments:
The workaround is possible. It should work if you:
People in the linked bug writes that it works. However, I've noticed that you have to have 2FA disabled on your Google account. Otherwise Google won't let you to enable "less secure apps". I haven't tried the workaround because I don't want to lose security 2FA gives you.
For the explanation of why this is happening see this Daniel Vratil's blog post: https://www.dvratil.cz/2019/08/kontact-google-integration-issue/
Check your gMail on another device. Is it prompting you to approve a login?
It sounds like you may have to wait for Google to verify KMail as an app that can use Google Sign In.