GNOME Online Accounts has been ported from GTK3 to GTK4 for GNOME 46. I believe there were other API changes at the same time. In summary, the GNOME Online Accounts library is no longer compatible with budgie-control-center, cinnamon-control-center and unity-control-center.
When I brought up my concerns about this change with the project’s developers, they pointed out that it is problematic for non-GNOME projects to be using GNOME Online Accounts directly anyway because of the limited use OAuth keys owned by the GNOME Foundation for access to Google, Microsoft, etc. services.
The other desktop projects have benefited because they were using old forks of gnome-control-center and things have seemed to work so far, but none of those control-center forks are using GTK4 so it’s not feasible to backport gnome-control-center 46’s implementation now.
As paths forward, desktop developers could try to use the Account SSO API. I believe this is used by KDE/Kubuntu and is related to the Ubuntu Online Accounts system Ubuntu Desktop used in the Unity days. That might be best since it appears to be somewhat cross-desktop. I suppose it would also be possible to rename and fork gnome-online-accounts 45 but developers will definitely need to register different OAuth keys than the existing GNOME keys and work with providers to set suitable limits.
I apologize for the late notice about this issue. I am uploading the new gnome-online-accounts to Ubuntu 24.04 LTS today because Ubuntu Desktop needs features from the new library version.