  WASP-39b is one of the first extrasolar giant gas planets that has been
observed within the JWST ERS program. Fundamental properties that may enable
the link to exoplanet formation differ amongst retrieval methods, for example
metallicity and mineral ratios.
  In this work, the formation of clouds in the atmosphere of WASP-39b is
explored to investigate how inhomogeneous cloud properties (particle sizes,
material composition, opacity) may be for this intermediately warm gaseous
exoplanet. WASP-39b's atmosphere has a comparable day-night temperature median
with sufficiently low temperatures that clouds may form globally. The presence
of clouds on WASP-39b can explain observations without resorting to a high (>
100x solar) metallicity atmosphere for a reduced vertical mixing efficiency.
The assessment of mineral ratios shows an under-depletion of S/O due to
condensation compared to C/O, Mg/O, Si/O, Fe/O ratios. Vertical patchiness due
to heterogeneous cloud composition challenges simple cloud models. An equal
mixture of silicates and metal oxides is expected to characterise the cloud
top. Further, optical properties of Fe and Mg silicates in the mid-infrared
differ significantly which will impact the interpretation of JWST observations.
We conclude that WASP-39b's atmosphere contains clouds and the underdepletion
of S/O by atmospheric condensation processes suggest the use of sulphur gas
species as a possible link to primordial element abundances. Over-simplified
cloud models do not capture the complex nature of mixed-condensate clouds in
exoplanet atmospheres. The clouds in the observable upper atmosphere of
WASP-39b are a mixture of different silicates and metal oxides. The use of
constant particles sizes and/or one-material cloud particles alone to interpret
spectra may not be sufficient to capture the full complexity available through
JWST observations.
