How to use KMail with Gmail 2-factor auth? I was able to set up Gmail accounts in 5.13 Kubuntu 18.10 but starting January it is not syncing anymore. It seems the authentication token is expired for all my 3 gmail accounts. However there is no pop up im Kmail indicating this. I also tried to reauthenticate but the Imap setup dialog has the password grayed out. I deleted all accounts using gmail 2-factor. Now I cannot even add accounts either the web view is crashing oder if I am able to add the imap account there is no sync. I tried 13.5, 14.5 and 14.90 beta from the Kubuntu PPA.

That's odd...I thought I read somewhere that Kmail was updated to use the Auth method that Google requires for gmail access? Maybe turn off the 2 factor process? Not sure as I don't use Kmail, I've been a Thunderbird user instead. Maybe go to Google help pages for gmail and search for Kmail issues? Or perhaps remove and add the gmail account again in Kmail to use the new process?
Sorry I can't help more...

Disabling 2-factor auth is no option for me. There is the fallback of generating an app password, but this is not working with Kmail. As soon as one enters imap.gmail.com as server the password and auth method gets grayed out and a web view is started for getting the auth token. However this always crashes. Manual entering gmail preferences is not possible anymore. Hence Kmail is useless together with gmail.

Sorry can't help with Kmail setup. Perhaps see if you can contact the KDE developers directly with the issue as it's actively updated so they'll want to have it work with Gmail. Search here for user Progdan (?) or skim through the Kmail posts for contact info.

I am now using Arch and Oauth is working there. Unfortunately it is broken in Kubuntu since a while and nobody fixing it.