Unable to load the kernel module 'nvidia.ko'

I followed the most excellent guide from Artofserver how to install a GPU with Proxmox, it worked just fine.
But this was a couple of weeks back when my GPU was too old... or the drivers were too old.
So I bought a GPU that is supported by the newest driver atm. Before I tried this I did run the nvidia-uninstaller script.
Swapped the GPU and tried to install the latest driver to date.
The building of the modules starts and gets interrupted with an error:
ERROR: Unable to load the...

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