kdepim-runtime is compiled with XOAUTH2 support, which produces libkdexoauth2.so, libkdexoauth2.so.3 and libkdexoauth.so.3.0.0 files. This is a SASL2 plugin and SASL2 looks only for "*.so" names (without soversion). kdepim-runtime does not include this file, so SASL2 does not load the XOAUTH2 plugin, which breaks Gmail login for all users. Most probably affects Dev stable and Dev unstable too.
I can confirm this - found this morning after upgrading neon/user that 'saslpluginviewer -c' does not list kdexoauth2. After creating a symlink manually, # cd /usr/lib/x86_64-linux-gnu # ln -s libkdexoauth2.so.3 libkdexoauth2.so kmail started working normally with GMAIL again
fix is building
This has reoccured with KDE 6 release. I had to create the symlink manually.
Also kpim6-libsasl2-modules-kdexoauth2 package was not installed during upgrade and I had to install it manually.