ghtester suggested writing LE 9.2.6 to a USB stick
- this had exactly the same result as using the SD card.
Klojum suggested booting on a (non-4K) PC monitor or other TV.
- I only have TV monitors that support VGA or Display Port. Using my HDMI cable and an HDMI/DP adapter resulted in nothing on the screen (not even the RPi startup screen).
- I have only one TV that has HDMI.
Klojum also suggested that I update the firmware using RaspOS
- I had done this already; see my first post on May 5th.
Since the RPi 4B worked fine with RaspOS, my supplier for the RPi suggested that I modify config.txt on the LE 9.2.6 SD card, to force the correct CEA mode (i.e., to disable auto-detect), but this also had no effect.
hdmi_group:0=1 # Use CEA
hdmi_mode:0=16 # mode 16: 1920x1080 @ 60Hz 16:9, clock:148MHz progressive
Finally, ghtester suggested using the nightly build for LE 10. This solved the problem, but puts me on the bleeding edge, with alpha software. I have no problem with this, but the other users in my house are not as comfortable with technology.
Clearly, there is something that LE 9 does not do, and LE 10 does do, in the boot-up sequence, that is getting in the way of successful initialization of a new system card. If anyone can put me in touch with the appropriate system development person(s), I would be happy to serve as a debugger, to determine where the failure is. Perhaps the fix is something that could go into LE 9.2.7...