I accidentally discovered a partial "hack" (a half hack, if you will). On my M1 Mac Studio, at least, any song can be rated with half-stars as long as I'm viewing it in "Songs" (as opposed to in its album or playlist settings, where Music still insists on full stars only). I'm on 15.1.1 right now, but I think I stumbled upon this at an earlier version of Sequoia. It's only a half hack, because even after tweaking a rating, say, from 4 stars to 4.5 while in Songs, the same track will continue to default to a full star neighbour when I view it elsewhere. Still, it's occasionally helpful when I'm reviewing my library in "Songs" mode. One can continue to hope that some day Apple will acquire the "intelligence" to make this very useful user customization available across all Apple Music sorting categories. I get that they're on a limited budget, but I think this should be a priority.