RPi4 Dual Screen not working with Waveshare LCD101-1026x600 and normal Monitor

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Hi,

I have tried to get a Dual screen setup with a Waveshare LCD101-1026x600 and a normal Monitor (1440x900) working but when I try to use them booth the LCD101 stays black or is stuck at the rainbow screen. If I remove the monitor from hdmi1 and reboot it works. If I unplug the LCD101 and connect the monitor on hdmi0 it also boots with the settings of the LCD101. I have tried different settings:

1st:
display_rotate:0=0
hdmi_group:0=2
hdmi_mode:0=87
hdmi_cvt:0 1024 600 60 6 0 0 0
hdmi_drive:0=1
hdmi_force_hotplug:0=1

display_rotate:1=0
hdmi_group:1=2
hdmi_mode:1=47
hdmi_drive:1=1
hdmi_force_hotplug:1=1

2nd:
[HDMI:0]
display_rotate=0
hdmi_group=2
hdmi_mode=87
hdmi_cvt 1024 600 60 6 0 0 0
hdmi_drive=1
hdmi_force_hotplug=1

[HDMI:1]
display_rotate=0
hdmi_group=2
hdmi_mode=47
hdmi_drive=1
hdmi_force_hotplug=1

somewhere someone mentioned the option:
max_framebuffers=2
but that does not work either I also can't find this option in the docs

https://www.raspberrypi.org/documentation/configuration/config-txt/video.md
https://www.raspberrypi.org/documentation/configuration/config-txt/conditional.md

Then I have tried:
framebuffer_priority=2
but that also does nothing expect that I can see all console output at start

The site of the LCD101 is here:
https://github.com/waveshare/LCD-show

I don't know if I should have posted this on https://github.com/raspberrypi/linux/issues if yes then sorry.

Another thing that I have seen is when I only unplug the LCD101 from hdmi0 but let the monitor on hdmi1 and turn on the screen it will also stay black. I have waited some time because I have thought the second display turns only on when raspbian is completely up but nothing happened. I have then switched the monitor cable to hdmi0 but nothing happened there either.