Under the hood what this is doing is unlocking a "keyring" managed by the system and often tied to your user account. There are many interfaces, KWallet, Seahorse (Gnome version), and others, but it appears that however Plasma is configured it didn't get linked to your user login to unlock the keyring at the same time. Gnome handles this for you if you delete a keyring via Seahorse, and then it will set up a new "Login" one, which is where Chromium/NetworkManager and others usually store secrets.