Black screen on boot

I have a strange problem. When I boot my laptop with an external monitor attached using HDMI, it works perfectly, starts the sddm login screen and then boots into KDE. But when I boot without an external monitor, it boots into black screen.

However, I can switch to alternate console and login in the terminal. I think it is not entirely a graphics driver related issue, if at all. Because, from the alternate console I can login and then I am able to use startx to directly start the DE. There is no login screen though. That is probably because I already logged into the console before starting the DE. Some details which might be relevant are below:

I am using:

Linux axion 5.8.9-2-MANJARO #1 SMP PREEMPT Sun Sep 13 13:36:33 UTC 2020 x86_64 GNU/Linux

My laptop has a intel-nvidia hybrid graphics hardware:

00:02.0 VGA compatible controller: Intel Corporation UHD Graphics 630 (Mobile)
01:00.0 VGA compatible controller: NVIDIA Corporation TU106M [GeForce RTX 2070 Mobile] (rev a1)

I have proprietary nvidia prime enabled driver installed uusing mhwd:

> Installed PCI configs:
                  NAME               VERSION          FREEDRIVER           TYPE
     video-modesetting            2020.01.13                true            PCI
video-hybrid-intel-nvidia-450xx-prime            2019.10.25               false            PCI

My primary screen is 4K (3850 × 2160)