Relativistic nucleus–nucleus collisions offer a unique possibility for studying nuclear matter under the influence of high temperature and pressure. During the collision a system of interacting nucleons, resonances, and mesons, called hadronic fireball, is created.\par
The Dielectron Spectrometer HADES operated at the SIS18 synchrotron of FAIR/GSI Darmstadt recently provided new intriguing results on production of electron pairs and strangeness from nucleus-nucleus collisions, as well as from reference elementary reactions, in energy region of $1 - 2$~A~GeV. At 2019 it was complemented by a new electromagnetic calorimeter based on lead-glass modules, which allows to measure production of the $\pi^0$ and $\eta$ mesons via their two-photon decay. In this energy range, $\pi^0$ and $\eta$ mesons are the most abundantly produced mesons carrying information from the hadronic fireball. In addition, the knowledge of the neutral meson production is a mandatory prerequisite for the interpretation of dielectron data and at the same time almost no respective data are presently available for this energy range.\par
Recent result on $\pi^0$ production in Ag + Ag collisions at 1.58~A~GeV with $14\times10^9$ collected events will be presented . The yields, transverse mass and rapidity distributions will be shown and compared with existing data from other experiments as well as with transport model calculations.