Unable to select Nvidia proprietry driver (greyed out)

I have just completed a fresh installation of Ubuntu 20.04 LTS. I am using a minimal install and enabled the use of proprietary drivers during installation.

Upon boot and logging in my resolution was set at 1024x768 and I cannot change it. I went to the Additional Drivers page of Software & Updates, but continuing to use my manually installed driver is both the selected option and only one that is not greyed out.

I have read that the fix for this is sudo ubuntu-drivers autoinstall, but this then prompts me to Media change: please insert the disc labeled 'Ubuntu 20.04.3 LTS _Focal Fossa_ - Release amd64 (20210819)' in the drive '/cdrom/' and press [Enter], but this CD media does not exist (I installed via USB) and I have not seen mention of this on other topics. Inserting this does not help.

How do I resolve my graphics issue and switch to the proprietary drivers listed?

I am using a GeForce GTX 980 Ti.

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