Howdy,
Dan helped me figure out why Gmail IMAP wasn't working for me with master.
Make sure you are properly setting $SASL_PATH
to double-check, locate where you have libkdexoauth2.so.3 installed.
it should be in ${KDE_PREFIX}/lib64/sasl2
I fixed [1] accordingly.
[1]
https://community.kde.org/KDE_PIM/Development/Start#Setting_up_environment