I think OP is mixing up IRC and Matrix. IRC indeed does require you to be online to receive messages (but there are ways around that), but matrix loads your messages offline just fine.
Checked it now and I have 3k unread messages on the lemmy support chart.
Oh, so that explains why the ratio of favorites/boosts is so low on mastodon. I thought it was just a culture thing, where people rarely left likes on posts.
Turns out it was just a software quirk.
Don’t worry, war is bad, but planes are rad.