The word "must" should only be used in the Military. Anywhere else, it is profusely out of place. In its stead, I recommend the term "requirement" and then cite an actual reference by the PO or someone officially representing the business requirements.
Can you explain why? I’ve definitely seen must used in non military contexts. It also seems really strict to limit musts to things specifically laid out in requirements, unless I’m just used to dealing with really loose requirements. My gut is that you’d run into two categories of shoulds, one which is a much bigger deal than the other.
