Hello, dear Debian developers! It seems that you updated TelepathyQt to v0.9.8, but you didn't update KDE Applications at least to v19.12.0. The mentioned bug fixed by this patch from an Arch developer: https://phabricator.kde.org/D25372 (released as v19.12.0).
- Bug#948907: ktp-call-ui: FTBFS: QDBusArgument: ... Dmitry Shachnev
- Bug#948907: ktp-call-ui is marked for auto... Alexander Akulich
- Bug#948907: marked as done (ktp-call-ui: F... Debian Bug Tracking System