raspberry 400 hdmi output does not follow config.txt

Question

Have my new raspberry 400 with current Raspberry OS and connected a TV by the official micro-HDMI-cable. There is no problem getting an image, but it always goes to 1080p@50 mode (TV tells me that, and the display is flickering). Tried different solutions, but none helped. In /boot/config.txt I have (tested with different combinations):

hdmi_force_hotplug=1
hdmi_ignore_edid=0xa5000080
hdmi_group=2
hdmi_mode=82
hdmi_force_mode=1

Tried also different groups and modes, like hdmi_group=1 and hdmi_mode=16.

kmsprint tells me 1920x1080i@50 on graphical display and 1920x1080i@60 on tty1.

What works (I use this as a workaround):

xrandr --output HDMI-1 --mode 1920x1080

What is wrong in /boot/config.txt?

Answer 1

Following the ideas from this post I found two (not really satisfying) solutions:

a) Add a desktop file in /etc/xdg/autostart with contents

[Desktop Entry]
Version=1.0
Type=Application
Name=xrandr1080p
Comment=
Exec=xrandr --output HDMI-1 --mode 1920x1080
Icon=preferences-desktop-display
Path=
Terminal=false
StartupNotify=false

After logging in to the graphical desktop, this will modify the mode to 1080p@60. But on tty it still is 1080i@60.

b) Use dtoverlay=vc4-fkms-v3d instead of dtoverlay=vc4-kms-v3d in /boot/config.txt. This works and respects the hdmi settings in config.txt. I do not know whether there are any drawbacks with this solution; but I do not use the raspberry for video works, and only need a working desktop and GUI.