I’m using Ubuntu 20.04 on a Dell laptop and after the latest kernel updates yesterday to version 5.8.0-45 my display port stopped working. It seems that internally the laptop screen is also using a displayport which is also not working. I only see the Dell logo on both screens (the external displays are Dell as well and are identical models). Only connecting an external display directly through the HDMI port on the laptop seems to work fine.
Initially the nvidia drivers were not correctly installed and in that situation things were reversed - the laptop screen and the displayport connected display worked fine while the HDMI connected display was not detected. After following the instructions on this post I managed to get the nvidia driver to work as expected. Since then only the HDMI connected display seem to work. I also tried downgrading the kernel to version 5.4.0-67 like suggested in this post, but it did not change anything visibly.
I’m attaching the nvidia error logs on both kernel version 5.8.0-45 and 5.4.0-67. There is an error in both of them saying that
ERROR: Kernel configuration is invalid. include/generated/autoconf.h or include/config/auto.conf are missing. Run 'make oldconfig && make prepare' on kernel src to fix it.
but I couldn’t fix that googling for solutions as none of them worked.