External monitor not detected while using proprietary drivers

Hi and welcome,

I think your general issue of

Is the same as in many other threads.
Quite simply - you are using a hybrid profile that by default uses the iGPU (amd), while at the same time you are plugging in your monitor to the dGPU (nvidia).

There are a number of solutions to this … see for example this thread and the responses there

optimus-manager is largely considered trash.
If you need a ‘switcher’ utility then alternatives exist like envycontrol.

But we should probably make sure to deal with whatever mhwd problem you may be having;

So can you please provide the actual logs here?

I can suggest sorting mirrors first as well;

sudo pacman-mirrors -f && sudo pacman -Syu
sudo mhwd -i pci video-hybrid-amd-nvidia-prime

PS.

This guide will also cover things like how to format code etc