Hi, I think this bug report should not belong to the plasma-settings package.
As you wrote, you are using SystemSettings, which is another app: let's think of plasma-settings as the settings app for a mobile system, while systemsettings is the settings app for a desktop system. On a mobile system, both are installed due to plasma-mobile's dependencies depending on systemsettings, but they are different packages.
As described in [1][2], both systemsettings and plasma-settings are not responsible themselves for managing OnlineAccounts: they are just exposing the available KCMs. In fact, I do not see the OnlineAccounts section inside systemsettings/plasma-settings on my system, unless I install the kaccounts-integration package.
Tbh I've no clue where this bug should be re-assigned. Looking at the attachment inside [3] bug report, looks like some kind of browser plugin is invoked to open the OpenDesktop login interface inside an X window... it could be Kaccounts, it could be KCM, it could also be that the login window does not support Wayland... have you tried launching systemsettings from the console and check if any error message is displayed when you try the OpenDesktop login?
Kind regards Marco [1] https://invent.kde.org/network/kaccounts-integration#kde-control-module [2] https://community.kde.org/Online_Accounts [3] https://bugs.kde.org/show_bug.cgi?id=438424
