Comment 9 for bug 1862764

I started using Ubuntu 22.04 and this issue started to occour.

The 'add-apt-repository' command adds the gpg key of the PPA repository in the trusted.gpg file (/etc/apt/trusted.gpg)

As commented above, the PPA repositories are not being included in the sources.list file (/etc/apt/sources.list) or in the directory /etc/apt/sources.list.d/<repo-name> with the parameter [signed-by=]

Workaround:
While the fix doesn't come, the way is to adapt the repository in this way:
1- $ sudo add-apt-repository ppa:author/project
2- $ apt-key list
3- $ gpg --export <repository-fingerprint> | sudo tee /usr/share/keyrings/<repo-name>.gpg
4- $ sudo nano /etc/apt/sources.list.d/repository-name.list
5- Find & Replace:
deb http://ppa.launchpad.net/author/project/ubuntu jammy main
by
deb [signed-by=/usr/share/keyrings/<repo-name>.gpg] http://ppa.launchpad.net/author/project/ubuntu jammy main

6- Save the changes and run 'sudo apt update' again