Lignocellulose biomasses (LCB) are abundant and sustainable reservoirs of fermentable sugars that can be exploited to produce bio-based fuels and chemicals. In the emerging context of a circular economy, the implementation of thermophilic microbes and enzymes can represent a greener tool for lignocellulose deconstruction. We described the biochemical characterization of enzymes secreted by a microbiome (named CMC-70), which was obtained after an enrichment at 70°C using spent mushroom substrate (SMS) and subsequently selected on carboxymethylcellulose (CMC) as a pure carbon source. The proliferation of the microbiome on SMS revealed the secretion in the supernatant of thermostable xylanases. These enzymes were mainly active from pH 5 to pH 10, with an optimum at pH 7. Xylanase activity was highest at 80°C, and the secretome retained more than 50% of its initial activity over two months when stored at 4 °C. Enzymes' hydrolytic potential was tested on pure and complex biomasses, highlighting the presence of a wide spectrum of glycoside hydrolase (GH) activities. These insights provide a framework for future formulations of more effective enzymatic cocktails for biotechnological applications. The research was granted by Next Generation EU in the context of the National Biodiversity Future Center (NBFC).