There are multi-virus tests. Not "an universal antigen test" (I think that'd be challenging, there are AFAIK hundreds of "normal common cold" viruses out there)

There are multi-virus tests. Not "an universal antigen test" (I think that'd be challenging, there are AFAIK hundreds of "normal common cold" viruses out there), but it's getting better. I got a 5-virus test for a study recently (Influenza A+B, Adenovirus, RSV, Covid). I haven't seen them to be sold for end customers. There are a few 4-virus tests on the market here, yet the legality is currently questionable here in Germany. (It seems there's an interpretation of the law that Influenza testing shall only be done by doctors.)