The PN51 models come with the same chassis from last year's PN50 models and only support the Zen 2 Lucienne Ryzen 5000U processors. Despite using the same Zen 2 cores as the Ryzen 4000U models, the Lucienne processors come with upgraded memory controllers and can be coupled with up to 32 GB of DDR4-3200 RAM plus up to 2 TB of storage. There also is support for up to 4x 4K monitors.
https://www.notebookcheck.net/Asus-announces-PN51-mini-PC-powered-by-AMD-s-Ryzen-5000U-processors.531293.0.html