Local first apps have some peculiar technical features, yes. I worked on CRDTs from maybe 2008 and in 2012 we made a collaborative editor. Local first, all data on the client, syncing by WebSocket. I remember when we debugged it we once had a problem resetting a document. It kept reappearing. The guilty was an iPad laying on the table face down. It synced all the data back. That was seriously different from e.g. Evernote that was losing data all the time. In our system, intentionally purging was really difficult.
Once we ran two weeks with a "poisoned" document that was crushing any server it was uploaded to. The user kept the tab open just working like nothing was happening. Then, we found the bug, but in theory we may have made the entire cluster restart all the time. Apart from electricity consumption, that would hardly change anything. The load and syncing time would be worse, but not by much.
With local-first, everything keeps working even without the server.
Here is the 2012 engine, by the way: