  Context. The soft excess, a surplus of X-ray photons above 2 keV with respect
to a power law, is a feature of debated physical origin found in the X-ray
spectra of many type-1 active galactic nuclei (AGN). The eROSITA instrument
aboard the Spectrum-Roentgen-Gamma (SRG) mission will provide an all-sky census
of AGN suitable for spectral analysis. Aims. The primary goal of this work is
to test a variety of models for the soft X-ray emission of AGN (thermal
emission, non-thermal emission, ionised absorption, or neutral partial covering
absorption) to help identify the physical origin of the soft X-ray spectral
complexity. Differences between these models are examined in the context of
this sample to understand the physical properties. Methods. We used Bayesian
X-ray analysis to fit a sample of 200 AGN from the eFEDS hard X-ray--selected
sample with a variety of phenomenological and physically motivated models.
Model selection was performed using the Bayes factor to compare the
applicability of each model. Results. We find that 29 sources have evidence for
a soft excess at a confidence level >97.5%, all of which are better modelled by
an additional soft power law than by thermal blackbody emission. We find 23 of
these sources prefer a warm corona model, while six sources prefer relativistic
blurred reflection. Additionally many sources show evidence for complex
absorption, with 29 preferring a warm absorber and 25 a partial covering
absorber. Sources with a soft excess show a significantly higher Eddington
ratio than those with warm absorbers. We discuss the implication of these
results for the physical processes in the central regions of AGN. Conclusions.
Spectral fitting with Bayesian statistics is ideal for the identification of
complex absorption and soft excesses in the X-ray spectra of AGN and can allow
one to distinguish between different physical interpretations. (Abridged)
