External SSD vanished after macOS update macOS 27 Golden Gate

Drive missing from Finder/Disk Utility/diskutil list entirely (not even "unmounted")? Check hardware detection first, in Terminal:

diskutil list

system_profiler SPThunderboltDataType SPUSBDataType

If Thunderbolt shows "No device connected" but other USB devices mount fine, the fault is that drive/cable/enclosure/hub. Not your Mac's ports or macOS itself.

My setup: SSD enclosure connected through a UGREEN Docking Station USB C into the Mac mini M4.

What fixed it here: connecting the drive (still through the hub) to a different Mac (a Macbook Pro in my case), then back to the original Mac mini. Mounted fine after.

It's likely the hub or enclosure needed its link/controller reset, which the second Mac triggered.