The instructions in the blog post worked for me but printed some deprecation warnings:
$ wget -qO - https://pkg.jenkins.io/debian-stable/jenkins.io-2023.key | sudo apt-key add -
Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).
OK
$
To avoid using deprecated functionality I downloaded the https://pkg.jenkins.io/debian-stable/jenkins.io-2023.key file and put it in /usr/share/keyrings/jenkins-keyring.asc and updated /etc/apt/sources.list.d/jenkins.list with:
deb [signed-by=/usr/share/keyrings/jenkins-keyring.asc] https://pkg.jenkins.io/debian binary/
I have no idea if this is the best way of doing things or not, but it solved the deprecation warning I was getting on Ubuntu 22.04.2 LTS x86_64.