I made it for my own Mac mini setup with NVMe external drives that are always plugged-in and behave like internal storage. Noject lets you protect those volumes and reject any normal eject/unmount attempts from Finder, Disk Utility, Terminal, and other apps.
It uses Apple's Disk Arbitration framework, protects volumes by UUID, and has an "Eject Once" bypass for when you really do want to disconnect something. It is privacy first and does not need to read the contents of your drives.
Available for lifetime and free/fair download from the website https://scaleninja.com/noject/