Generally, this is not really true. The point of CRDTs is that as long as all parties receive all messages (in any order), they should be able to recreate the same state.
So instead of merging changes on the server, all you need is some way of knowing which messages you haven’t received yet. Importantly this does not require the server to be able to actually read those messages. All it needs is some metadata (basically just an id per message), and when reconnecting, it needs to send all the not-yet-received messages to the client, so it’s probably useful to keep track of which client has received which messages, to prevent having to figure that out every time a client connects.
So instead of merging changes on the server, all you need is some way of knowing which messages you haven’t received yet. Importantly this does not require the server to be able to actually read those messages. All it needs is some metadata (basically just an id per message), and when reconnecting, it needs to send all the not-yet-received messages to the client, so it’s probably useful to keep track of which client has received which messages, to prevent having to figure that out every time a client connects.