Je ne peux plus faire des mises à jour

[stevef]

Your error messages indicates your system may have conflicting values for verifying the signal software. It is not obvious how this could have happened from those instructions.

We can try to sort the problem out, but debugging over a forum can be complex, slow and is not guaranteed to work.
The quickest option may be to begin again with a fresh installation, so if you wish to try that, let us know.

To try debugging the existing install please follow the suggestions below.

1) Did you notice any error messages while running the install instructions ?
2) Did you try any other methods to install the signal application ?
3) Try to verify that the install instructions worked as expected.

Open a terminal by pressing Ctrl Alt and T keys together.  In the new window, enter the commands below.
Copy and paste the results back in the thread.

This command will show the keys installed

Code:

ls -l /usr/share/keyrings/

This command will check that the key downloaded for signal is readable.

Code:

file /usr/share/keyrings/signal-desktop-keyring.gpg

This command will show repositories to check the signal got added in the expected place

Code:

ls -l /etc/apt/sources.list.d/

This command will show the contents of the signal file which may hold the conflicting signing information reported by the update/upgrade.

Code:

cat /etc/apt/sources.list.d/signal-xenial.list