The so-called "removable SSDs" in the Apple Mac Studio aren't actual SSDs but just raw storage modules. Apple silicon Macs do not use the standard NVMe protocol but instead use their own implementation via PCIe. This means, it is not possible to simply swap-out or add storage at whim to the Mac Studio without matching the exact capacity and vendor and doing a full DFU restore.
https://www.notebookcheck.net/Mac-Studio-SSD-does-not-work-on-NVMe-top-level-ARM64-SSD-controller-in-M1-Ultra-makes-it-nearly-impossible-to-swap-out-or-add-raw-storage-modules.609363.0.html