I can currently only install Tahoe 26.01 and cannot upgrade to 26.1. I’ve been troubleshooting for several days, and here is the status:
Clicking “Update” shows the process completing normally, but the system remains at 26.01 after reboot. The upgrade fails to apply.
A clean, full installation from the initial state fails to launch.
However, when I used a different external hard drive, I was able to install and use 26.1 successfully.
This leads me to suspect two potential issues:
A defect in the original Thunderbolt 5 cable or insufficient chip compatibility.
A driver bug in Tahoe 26.1, which has been widely reported by other users.