The 3rd trilateral meeting, involving parties from the University of Nova Gorica, SISSA and ICTP from Trieste and from the Jožef Stefan Institute in Ljubljana, will take place in the Lanthieri mansion in Vipava on September 15th, 2021. The talks will cover selected topics from astrophysics. In particular, the groups will discuss various ways to search for Dark matter candidates. This includes high-energy photon probes of ‘unusual’ dark matter candidates”, including primordial black hole searches via X-ray probes and the potential of ground-based instruments like HAWC, Tibet, LHAASO to look for heavy DM decay. Moreover, the group will study the use of multimessenger astrophysics to constrain Axion-Like-Particles and in general about LSST activities at UNG. Recent progress in the use of machine learning with Gaia data to constrain dark matter Galactic substructures will be presented as well as its impact in discovering faint Fermi LAT point sources (with implications for hidden DM signals) and/or the CTA sensitivity to multi-TeV DM.