SOLUTION (hopefully, I will report back if the issue happens again): If you're also experiencing this nieche issue you will probably have to reset your system, when doing an install using arch install and are in the part where you have to chose the driver DONT chose all drivers and choose proprietary nvidia drivers instead.
I recently updated everything on my PC and then after rebooting my external GPU (Geforce GTX 1070 connected via Thunderbolt, GIGABYTE GV-N1070IXEB-8GD) didn't display any output (But the fans still spin, light still lights up, display and cable work), but the internal one of my CPU (intel) still worked.
I am using Plasma (Wayland).
The connection is also connected authorized and trusted.
I already tried to downgrade my Nvidia drivers to the 580xx Versions but that apparently didn't do anything.
Whenever I try to run nvidia-smi it gives me the error message: "NVIDIA-SMI has failed because it couldn't communicate with the NVIDIA driver. Make sure that the latest NVIDIA driver is installed and running."
But dkms status doesn't give me any error messages ("nvidia/580.119.02, 6.18.2-arch2-1, x86_64: installed"
I also modified my grub file (this line: "GRUB_CMDLINE_LINUX_DEFAULT="quiet splash modprobe.blacklist=nouveau nvidia-drm.modeset=1 pci=realloc intel_iommu=off iommu=pt"")
Previously when my eGPU actually worked whenever I booted into the login screen it displayed a white noise screen until I logged in, I never thought to fix it though as it did not really disrupt my regular use.
Can anyone please help me to make my eGPU actually display an output again? (it is also just my best guess that this is because of the new driver, it could also be because of some other reason)