Pre-pandemic artificial MERS analog of polyfunctional SARS-CoV-2 S1/S2 furin cleavage site domain is unique among spike proteins of genus Betacoronavirus - BMC Genomic Data
Covid's S1/S2 furin cleavage site domain has only been found on one other virus... an artificial one.
It doesn't mean there aren't any viruses with it out there in the wild... but we haven't found any yet.