I think this may be an issue with Plasma 6.1, or at least a transition between Plasma/KF/Qt5 and 6 components. Kubuntu includes the online accounts packages by defualt
The packages set is different, as most of the ones with “6” don’t exist in 24.10/Plasma 6.1, but others that seem to be similar are present.
I just found an old neon iso with 6.1.x, I might check it out and see if it suffers the same fate as Kubuntu and/or compare packages