I attempted to install macOS from Recovery Mode on a new external SSD connected to my M4 Mac Mini. However, the system would not boot from the external drive at all. Each attempt resulted in the Mac entering Recovery Mode (startup disk).
When I selected the external drive again, the system prompted me to reinstall the operating system, which I did, but the issue persisted.
Here’s why, must use the Thunderbolt port to the far right (rear) of the M4 Mac Mini. Any other port in the rear other than caused the Mac to loop back into Recovery Mode.
This issue appears to be port related.
Additionally, when I manually selected the external drive from the boot selector (by holding down the power button at startup), the Mac loads into Recovery Mode, displaying the startup disk selection again.
DETAILS
M4 baseline model: 16 GB | 258 GB
macOS 15.1.
External Enclosure: 3.1 USB-C with a 1TB Samsung 870 EVO 2.5” SATA III SSD.