He's experiencing a known HW issue, most likely. There's a manual workaround for now: https://xnux.eu/log/#045
I'll implement a SW workaround eventually, but I'm still recuperating a bit from the work on the Pinephopne keyboard. Once it's released, donations will hopefully increase a bit again, and I'll be able to do more development other than a kernel maintenance.
Now there's also Pinephone Pro and Quartz64 based router sitting on my table which I'm mostly playing with these days, so I'm a bit torn on where to focus my energy next. :)
I recently watched a presentation [0] that focused on the pinephone state-of-affairs, and it did not leave me with the impression the dock couldn't display on a monitor.
Are you sure you're not just experiencing some pathological incompatibility problem? Or am I going senile and need to re-watch the video?
[0] https://www.youtube.com/watch?v=PuEL_GJ1Y2s