There aren't many announcements about it because it happens so frequently. It's been happening rather constantly since even before the expansion release.

But you can tell it's a DDoS because you get the error that happens when they are protecting the server and there is no other evidence of connection issues on your network. And when you login again there's often a queue and "limited information displayed" which you see as lots of ???. Often when this happens you can ask your FC, linkshells, NN or discord servers and find out other people had it too.

It also isn't necessarily always a DDoS on SE directly, but on one of the nearby nodes, so technically SE doesn't have to say they had a DDoS necessarily.