Yes, quite possibly. Sugar doesn’t just sweeten sorbet—it’s also responsible for sorbet’s structure, so not entirely sure what xylitol would do. Generally it’s not a good idea to replace sugar with xylitol like-for-like since it’s got a different structure. There are a bunch of xylitol-based sorbet recipes online and also give this a read on the basic science of sorbet making: https://www.seriouseats.com/2014/06/how-to-make-the-best-sorbet.html