  A wealth of extragalactic populations completely missed at UV-optical
wavelengths has been identified in the last decade, combining the deepest HST
and Spitzer observations. These dark sources are thought to be very dusty and
star-forming systems at 3<z<5, and major contributors to the stellar mass build
up. JWST is now promising to detect such objects well beyond the end of the
Epoch of Reionization. In this Letter we report an investigation of the deep
JWST survey in the SMACS0723 cluster, analysing NIRCam and MIRI images. We
search for sources in the F444W band that are undetected in the F200W
catalogues. We characterise the main properties of these sources via detailed
SED modelling that account for a wide set of parameters and star formation
histories, after a careful determination of their photometry. Among a robust
sample of 20 candidates, we identify a mixed population of very red sources. We
highlight the identification of candidate evolved systems, with stellar masses
M*~10^(9-11)Msun at 8<z<13 characterized by unexpectedly important dust content
at those epochs (Av up to ~5.8mag), challenging current model predictions. We
further identify an extremely red source (F200W-F440W~7mag) that can be
reproduced only by the spectrum of a passive, quenched galaxy of M*~10^11.8Msun
at z~5, filled of dust (Av~5mag).
