I tested a lot and there is a very high chance, that the problem is the DVI-monitor.
I tried 2 different card-brands, Transcend and Patriot
I tried 2 DVI-monitors and 1 HDMI-monitor
I tried 3 Armbian images
Every time I use a DVI-monitor the installation doesn't start with similar behavior of the power led of the monitor (on, off, different times)
At the end I tried the newest Armbian_22.08.7_Rpi4b_jammy_current_5.15.74_xfce_desktop.img.xz with an HDMI monitor and everything worked fine. Putting this card, working with HDMI, in another PI400 with a DVI-monitor, it doesn't boot and the power led blinks as described.
So maybe there is a developer, who can test with a DVI-monitor?
On the other hand, there is 2022-09-22-raspios-bullseye-arm64-lite.img.xz which works with DVI. So maybe comparing the code could help.
Of course I can do test with a special image, that outputs some log or use Bullseye to do some queries.