“Vanilla server” is a server that is a fresh OS install with no other previous application installs, passbolt or otherwise. Just “plain vanilla” OS and new, which makes it likely passbolt will not conflict with other unexpected packages.
Thanks for the informations you provided, indeed I should have explained what a vanilla server is, thanks @garrett for clarifying that.
Would it be possible for you to run a fresh new Ubuntu 22.04 virtual machine, but before doing anything you’ll run:
sudo apt update
sudo apt upgrade
Then, you should follow the three first steps as you did previously but if you have an error you will copy/paste it here, so it will be easier for us to understand what is happening.
I think that you may get an output with a lot of text with something like Bad checksum. Aborting at the bottom meaning that the needed repository failed to get added correctly.