I've been able to get Windows kernel debugging working on a 1980s style RS232 COM port since 1999.
That streak has ended this week with problem of both COM1 serial and Network debugging NOT working on low level kernel debug on my new hardware platform ASUS W790E Sage (undated to ASUS latest BIOS, Aug. 2024), with Win11 Hardware Abstr. Layer 10.0.22621.2506 (Win build 10.0.22631). In all prior Windows builds (not just checked builds), I've been able to stop the kernel at the boot message (which displays the time), prior to any of my driver debug output being invoked. I can never get that.
We run Visual Studio 2022, and (thanks in part to OSR training in 1999 and some years of experience), I have managed to get past the MS VS2022 kernel project bugs to get Visual Studio's "driver deployment" working from a Win10 host-dev machine to the TARGET machine (the ASUS 790), using BOTH the RS232 COM and the Network pathways (that is, I can build a new kernel driver on host-dev machine and install it on the target machine across COM1 port or Network) - however, NEITHER of those will break into the kernel at boot or any other time using WndDbg (same ver 10.0.22631). So, clearly there is no hardware problem as the communication from VS2022 "deployment tools" work with the target on serial and network.
The target ASUS Dev Manager shows the COM1 port as the familiar 1980s style "I/O Range 03F8x03FF" with IRQ 4
Asking for clues from a guru.