Solar flares are generally thought to be the impulsive release of magnetic energy giving rise to a wide range of solar phenomena. During its commissioning phase in 2020, the Spectrometer/Telescope for Imaging X-rays (STIX) on board the Solar Orbiter (SOLO) spacecraft clearly observed 26 microflares and demonstrated its capability to reconstruct spectra for larger (GOES B class and larger) events. In this study, we make use of these capabilities to perform flare plasma diagnostics for a well observed B6 event which has the best count statistics in this set of commissioning flares. As there is only limited data from other SOLO instruments available to complement these initial observations, we make use of observations from GOES and instruments onboard the SDO spacecraft to complement the STIX instrument. It is demonstrated that the high spatial resolution, high cadence AIA EUV data and the DEM reconstructed from the data is a valuable tool to complement observations from the STIX X-ray instrument as it allows to distinguish the different components of the multi-thermal flare plasma (e.g. flare kernels and loops) and to observe flare plasma outside the sensitivity range of X-ray instruments. The capabilities demonstrated here will be very usefull when Solar Orbiter enters its nominal science phase towards the end of 2021. The SDO/AIA instrument provides high resolution, high cadence EUV imaging that additionally allows to reconstruct the Differential Emission Measure (DEM) of the thermal flare plasma while GOES provides an spatially integrated measurement in two X-ray channels that can be used for plasma diagnostics.