 The MWI is wrong if there is a physical process of collapse of the wave function of the Universe to a single-world quantum state. Some ingenious proposals for such a process have been made (see Pearle 1986 and the entry on  collapse theories).  These proposals (and Weissman’s 1999 non-linear decoherence idea) have additional observable effects, such as a tiny energy non-conservation, that were tested in several experiments, e.g. Collett et al. 1995, Diosi 2015. The effects were not found and some (but not all!) of these models have been ruled out, see Vinante et al. 2020.