Hi there @DanAskew,

The error that you are seeing is for the Brightbox Ruby NG repository which you have added to your server and saying that this repository is not available for your current Ubuntu version.

You would need to remove the http://ppa.launchpad.net/brightbox/ruby-ng/ubuntu focal Release repository from your repository source list and then run sudo apt update.

To do so first run:

apt policy

Thich will list all of the PPA repositories that you have.

• Then find the exact PPA repository that you want to remove and run the apt-add-repository but add the --remove flag:

sudo apt-add-repository --remove ppa:brightbox/ruby-ng

Finally, you will need to run:

sudo apt update

After that apt will start working as normal.

Let me know how it goes.
Regards,
Bobby