You can use a bouncer on IRC to retain messages while you were offline. In reality, it's the same with every other network: you need a server which receives and retains messages while you're offline.

With WhatsApp, Discord, etc, that server is provided by Facebook, Discard respectively. With XMPP, Matrix, that server is the instance in which you have an account or where the channel is hosted.

With IRC, you use a bouncer. What makes IRC unique is that a bouncer is _optional_. You can even join a channel without an account and without a server which keeps logs while you're offline. This ephemeral level of joining doesn't exist in WhatsApp, Discord, XMPP, Matrix, etc.

And, btw, this is not a new thing: I first saw bouncers 15 years ago and they weren't even new back then.