This always takes me a while to figure out when installing a new system so here is a foolproof guide to do this right once and for all. Kudos to all the people in this Manjaro thread. However, this should work on any system with KDE and systemd.
Make sure to install required packages:
sudo pacman -Syu --needed kwallet5 ksshaskpass kwalletmanager kwallet-pam signon-kwallet-extension