It’s not connectivity issue, ping and traceroute are going to succeed because they don’t require ssl/https. However, pacman/pamac/yay tries to download files over a secure https-connection. This requires that your system trusts the certificates of the sites you are downloading stuff from. If the certificates are expired, self signed or misconfigured, the https-connection is not possible and you can only use plain insecure http-connection.
Because AUR works for the rest of us and your downloads fail also from all repository sites, we can safely assume that the problem is in your network. For some reason your network has stopped trusting some big root CA, and https doesn’t work you in huge sections of internet.
So, you need to add a root CA certificate to your trusted certificates. Then your internet starts working normally and you can access AUR.