  A search for full energy depositions from bosonic keV-scale dark matter
candidates of masses between 65 keV and 1021 keV has been performed with data
collected during Phase II of the GERmanium Detector Array (GERDA) experiment.
Our analysis includes direct dark matter absorption as well as dark Compton
scattering. With a total exposure of 105.5 kg yr, no evidence for a signal
above the background has been observed. The resulting exclusion limits deduced
with either Bayesian or Frequentist statistics are the most stringent direct
constraints in the major part of the 140-1021 keV mass range. As an example, at
a mass of 150 keV the dimensionless coupling of dark photons and axion-like
particles to electrons has been constrained to $\alpha$'/$\alpha$ <
8.7x10$^{-24}$ and g$_{ae}$ < 3.3x10$^{-12}$ at 90% credible interval (CI),
respectively. Additionally, a search for peak-like signals from beyond the
Standard Model decays of nucleons and electrons is performed. We find for the
inclusive decay of a single neutron in $^{76}$Ge a lower lifetime limit of
$\tau_n$ > 1.5x10$^{24}$ yr and for a proton $\tau_p$ > 1.3x10$^{24}$ yr at 90%
CI. For the electron decay e$^-\rightarrow\nu_e\gamma$ a lower limit of
$\tau_e$ > 5.4x10$^{25}$ yr at 90% CI has been determined.
