Replaceable SSDs are coming for the new Apple Mac mini. While the new mini-PC supports removable storage, Apple does not offer replacement parts directly. Thankfully, the team behind the Studio Drive project for the Mac Studio has already confirmed plans to provide an equivalent solution for the new Mac mini.https://www.notebookcheck.net/Replaceable-SSDs-coming-for-new-Apple-Mac-mini.916943.0.html
Mini M4 and M4 Pro have different design storage cards, given how long it took for that shop to come up with M1 and M2 Studio storage cards and given it's not as easy and straightforward as just popping in another NVME SSD and their rather steep pricing then there might not be as large demand for these Mini cards.