I think certs have expired somewhere. I have tried the post that says same thing among many other things and so far I have not fixed it yet.
This is the error:
sudo apt-get update Hit:1 http://gb.archive.ubuntu.com/ubuntu focal InRelease Hit:2 Index of /repos/code/ stable InRelease Hit:3 Index of /graphics-drivers/ppa/ubuntu focal InRelease
Hit:4 Index of /utappia/stable/ubuntu focal InRelease
Hit:5 Index of /node_14.x/ focal InRelease
Ign:6 https://apt.syncthing.net syncthing InRelease
Err:7 https://apt.syncthing.net syncthing Release
Certificate verification failed: The certificate is NOT trusted. The certificate chain uses expired certificate. Could not handshake: Error in the certificate verification. [IP: 126.96.36.199 443] Hit:8 https://dl.yarnpkg.com/debian stable InRelease
Hit:9 https://packagecloud.io/slacktechnologies/slack/debian jessie InRelease Reading package lists… Done E: The repository ‘https://apt.syncthing.net syncthing Release’ no longer has 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.
Running the following it looks like a root cert expiry:
$ openssl s_client -connect apt.syncthing.net:443 CONNECTED(00000003) depth=2 C = US, O = Internet Security Research Group, CN = ISRG Root X1 verify return:1 depth=1 C = US, O = Let’s Encrypt, CN = R3 verify return:1 depth=0 CN = apt.syncthing.net verify return:1
Certificate chain 0 s:CN = apt.syncthing.net i:C = US, O = Let’s Encrypt, CN = R3 1 s:C = US, O = Let’s Encrypt, CN = R3 i:C = US, O = Internet Security Research Group, CN = ISRG Root X1 2 s:C = US, O = Internet Security Research Group, CN = ISRG Root X1 i:O = Digital Signature Trust Co., CN = DST Root CA X3
This indicates it is expired I think too:
Apologies if this is not related to syncthing but it seems like syncthing repo is the only one throwing this error.