I faced this issue today repeatedly, when trying to add jitsi keys on my server. i added logs for reference below. @damencho
root@ip-X.X.X.X:~#curl https://download.jitsi.org/jitsi-key.gpg.key | sudo sh -c 'gpg --dearmor > /usr/share/keyrings/jitsi-keyring.gpg' % Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 3071 100 3071 0 0 174 0 0:00:17 0:00:17 --:--:-- 910
root@ip-X.X.X.X:~# echo 'deb [signed-by=/usr/share/keyrings/jitsi-keyring.gpg] https://download.jitsi.org stable/' | sudo tee /etc/apt/sources.list.d/jitsi-stable.list > /dev/nul
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root@ip-X.X.X.X:~# sudo apt update
Hit:1 http://ap-south-1.ec2.archive.ubuntu.com/ubuntu bionic InRelease
Hit:2 http://security.ubuntu.com/ubuntu bionic-security InRelease
Hit:3 http://ap-south-1.ec2.archive.ubuntu.com/ubuntu bionic-updates InRelease
Hit:4 http://ap-south-1.ec2.archive.ubuntu.com/ubuntu bionic-backports InRelease
Ign:5 https://download.jitsi.org stable/ InRelease
Err:6 https://download.jitsi.org stable/ Release
Certificate verification failed: The certificate is NOT trusted. The certificate chain uses expired certificate. Could not handshake: Error in the certificate verification. [IP: X.X.X.X 443]
Reading package lists... Done
E: The repository 'https://download.jitsi.org stable/ Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.