It certainly points to a hardware-level fault rather than Windows or software.
- Freezes at login screen or shortly after desktop loads
- Fresh Windows 11 install does not help
- Returned twice unrepaired
All these indicate a Hardware fault.
This may be a faulty RAM, Failing SSD, Power / voltage regulation fault, Intel iGPU driver / firmware-level issue.
Try to boot into Safe mode -If Safe Mode also freezes → 100% hardware.
Open Event Viewer (if possible) and look for:
Kernel-Power
WHEA-Logger
Machine Check Exception