Ubuntu install process not working

Starting from this repo, I found installation instructions here: https://vdirsyncer.pimutils.org/en/stable/installation.html

I click on Ubuntu, which takes me to https://packagecloud.io/pimutils/vdirsyncer

I run the quick install script from that page:

curl -s https://packagecloud.io/install/repositories/pimutils/vdirsyncer/script.deb.sh | sudo bash

Which adds the repository https://packagecloud.io/pimutils/vdirsyncer/ubuntu

Then I run apt-get update && apt-get install vdirsyncer-latest (This complains that permission is denied, so I tried it with sudo)

This fails with:

E: The repository 'https://packagecloud.io/pimutils/vdirsyncer/ubuntu hirsute Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.

I tried overriding this security check, and even then the installation doesn't work. It seems that there may be something wrong with the installation instructions, if not, the repo configuration.

Start by checking the installation instructions at vdirsyncer.pimutils.org/en/stable/installation.html and the linked Packagecloud repository configuration. Reproduce the Ubuntu hirsute failure with the documented script and apt commands, then verify that the installation path works without the missing Release-file error.