Display omitted •Agro-industrial byproducts valorization through fungi bioconversion.•Peach palm shells opening prospects to livestock and circular bioeconomy.•Nutritional high-value bioproducts (SSF and SMS) for beef cattle diets.•Digestibility rate maintenance and mushroom β-glucans inclusion on cattle diets.•Bioproducts can help with ruminant GHG emissions mitigation. This paper aims to develop and assess the in vitro effects on ruminal fermentation and greenhouse gas parameters of new bioproducts for beef cattle diets, carried out by solid-state fermentation of peach palm shells colonized by Lentinula edodes (SSF) and after Shiitake mushroom cultivation in axenic blocks (SMS). In vitro experiments were performed to assess the in vitro gas production, digestibility, and fiber degradation of formulated total diets. Bioproducts presented high β-glucans (9.44–––11.27 %) and protein (10.04–––8.35 %) contents, as well as similar digestibility to conventional diets. SMS diet had the lowest methane and carbon dioxide (19.1 and 84.1 mM/g OM) production, and the SSF diet presented lower carbon dioxide production (98.9 mM/g OM) than other diets, whereas methane was similar. This study highlighted a sustainable use of byproducts for beef cattle diets, promising for digestibility, nutritional value, β-glucans incorporation, and environmental impact mitigation, favoring the circular bioeconomy.