The authority, exactly
No job offer and no sponsor are required on this route. There are two ways in: a qualifying prize on the Home Office's own published list of eligible prestigious prizes, or an endorsement from the body responsible for your field. The three fields are academia or research, arts and culture, and digital technology; each has its own endorsing body, and the criteria differ by field. The same post-Brexit rule applies here as on the Skilled Worker visa: an EU/EEA citizen without EU Settlement Scheme status needs this route (or another one) like any other non-British, non-Irish national.